How Lakes Differ
Types of Water Bodies
Susanna Scott | Miami University
Lakes vs. Ponds
Both lakes and ponds are standing or slow-moving bodies of water. There are no official or scientific differences between lakes and ponds. Lakes are larger than ponds, but size is relative. What would be considered a pond in one region might be considered a lake in another. In general, water bodies that are considered lakes in dry areas would only be considered ponds in regions with abundant water resources where there are more (and larger) bodies of water. Despite the lack of official characteristics, there are several questions that are used to generally distinguish ponds from lakes:
- Does light reach the bottom of the deepest point of the water body?
- Does the water body only get small waves (i.e., smaller than 1ft/30cm in height)?
- Is the water body relatively uniform in temperature?
If these questions can be answered with a “yes,” the water body is likely a pond and not a lake.1
Ponds are often overlooked as habitats and sources of biodiversity, but they play many important roles in the landscape. Many types of organisms spend at least part of their life in pond habitats, which function as important breeding grounds. Amphibians spend their juvenile stages in ponds, as do many insects. Some ponds, like vernal pools (Figure 1) are temporary and only filled with water for part of the year. However, theses pools are still teeming with life and are inhabited by organisms such as faerie shrimp, salamanders, and wood frog tadpoles while they are inundated with water. Ponds also function as important stopover spots for migrating birds. These spots provide places to rest, as well as a source of food for migrating waterfowl.2
Ponds also provide many uses for society. They are used for agricultural irrigation, nutrient and sediment retention, recreation, livestock, fish, wildlife protection and production, and aesthetic appeal. Threats to pond quality include, nutrient loading, pollution, acid rain and invasive species.3
Lakes vs. Rivers
Lakes and ponds are standing bodies of water while rivers and streams are distinguished by a fast-moving current. While there appear to be clear distinctions, the differences become subtle in regions where rivers widen and current slows such that the river could be considered a lake or a pond. Additionally, rivers may occasionally form lakes such as oxbow lakes when portions of a river become geologically separated from the main flow path over time.
River systems make up about 0.0001% of the Earth’s water. While this may not seem like much, rivers drain more than 75% of the Earth’s surface. Rain and other types of precipitation move water overland, through terrestrial ecosystems and into river systems. The resulting runoff brings inputs of sediments, nutrients, and materials into the river, causing running waters to be highly influenced by their surrounding landscapes. The flow of river systems carries the sediments, nutrients, and other materials through the landscape and into other systems, providing vital linkages between the land, lakes, wetlands and oceans. It is because of this that rivers are often referred to as the environment’s circulatory system.5
Lakes vs. Reservoirs
Reservoirs, also called impoundments, are man-made lakes. Often, reservoirs can be thought of as a combination of lakes and rivers because they were created by building a dam and flooding a river valley. This damming and flooding creates an artificial lake, filled by the river inflow, with the same qualities of rivers and lakes.
The upstream section of the reservoir has predominantly river-like qualities, meaning there is often still some current, and the organisms in this section are usually those found in rivers. As the water moves closer to the dam, the current slows, and the reservoir becomes more lake-like. At this point, many of the sediments and materials carried by the river settle to the bottom of the reservoir. Many of the organisms inhabiting this region of the reservoir are those more typically found in lakes.
However, some reservoirs maintain river-like qualities throughout. The degree to which riverine properties dominate the reservoirs is often a function of the size of the impounded river and the amount of time water spends in the reservoir (termed residence time). Reservoirs with a short residence time are more river-like while reservoirs with a long residence time are more like natural lakes.
Reservoirs are built for many uses. Some are built strictly for recreation (such as fishing and boating) or to control floods. Others are built to store water that may be used for drinking water and irrigation. Finally, hydroelectric dams use the flow of water over turbines to generate electricity. 6
Freshwater vs. Saline Lakes
People are most familiar with freshwater lakes. Chances are the lake closest to you is a freshwater lake. But some lakes are extremely salty. These are called saline lakes. Although freshwater lakes often have minor amounts of dissolved salts in them (less than 1-3 g/L), saline lakes have more than this (between 3 and 300g/L). 7 Saline lakes are often found in arid environments where water only leaves lakes through evaporation or seepage into the ground. This evaporation concentrates salts and other chemicals in the water over time.
Although many freshwater lakes and rivers drain into the ocean, saline lakes are formed when they are the endpoint to river flow. These lakes are known as endorheic (which means terminal), and are sometimes referred to as inland seas.8 Endorheic lakes usually form because they are at the lowest point in the landscape and are found in basins throughout the world. Well-known endorheic lakes include the Dead Sea (Israel/Jordan), the Great Salt Lake (Utah), Mono Lake (California) and the Caspian Sea (Eurasia).
Saline lakes such as the Great Salt Lake in Utah provide important habitat for many kinds of organisms. Some saline lakes are too salty to support anything but algae, but lakes such as the Great Salt Lake are habitats for crustaceans including brine shrimp. The shores and waters of these lakes also provide valuable habitat and breeding territory for birds such as shore birds and waterfowl.9
Inland seas are an important source for mineral trade and often have a great cultural significance. These lakes however are very sensitive to changes in climate. Because of high rates of evaporation in the areas they are located, even small reductions in precipitation can drastically reduce their size. With the reduction in size due to decreased inputs of freshwaters, salinity concentrations increase, which can change the biota and lead to decreased biodiversity. 5
- 1. Bronmark C. and H. Lars-Anders. 2004. Biology of Lakes and Ponds. Second ed. New York.
- 2. California wetlands information system. 2002. Retrieved online at: http://ceres.ca.gov/wetlands/whats_new/vernal_sjq.html
- 3. Oerthi et al. 2005 Conservation and monitoring of pond diversity: Introduction. Aquatic Conservation: Marine and freshwater ecosystems.
- 4. Vernal Pool. Bureau of Land Management. Retrieved online at: http://www.blm.gov/or/resources/recreation/tablerock/images/vernal_pool_lg.jpg
- 5. Wetzel, R.G., 2001, Limnology Lake and River Ecosystems, New York
- 6. Kalff, J., 2001, Limnology, Prentice Hall, NJ
- 7. Saline Lakes. 2006. Retrieved online at: http://www.chebucto.ns.ca/ccn/info/Science/SWCS/saline1.html
- 8. Dodds, W.K., 2002, Freshwater Ecology, Concepts and Environmental Applications, San Diego
- 9. U.S. Geological Survey. Birds and Great Salt Lake. 2009. Retrieved online at: http://ut.water.usgs.gov/greatsaltlake/birds/
- 10. Endorheic basins of the world. Retrieved online from: http://simple.wikipedia.org/wiki/Endorheic_basin
Jael Edgerton | Kent State University
Glacial lakes are common in North America as in other regions formerly traversed by the many glaciers of the last ice age. The grinding weight and pressure of encroaching and retreating ice sheets carved many depressions in the Earth’s surface, where melting ice then collected to form lakes. When ice sheets moved over flat rock surface with weakened areas of fissures, the rock could splinter and loosen to form the basin of “glacial scour lakes,” such as the Great Lakes in the U.S. and Canada1. Glacial lakes are often surrounded by other geological evidence of glacial scour.
When glacial scour action has formed a circular depression in a mountain valley, this type of scour is termed a cirque lake or tarn. Occasionally, a string of cirque lakes will form in adjacent mountain valleys to create successive “paternosters lakes”2. These lakes are often extremely clear, cold, and sensitive to environmental disturbances.
Several other types of lakes can form by glacial action and rocky debris gathered by glacial movement. Lakes can form from depressions or dams generated by glacial concentration of rocks and soils; these are referred to as moraine lakes because they form from the rock piles, or moraines, generated by glaciers. When a large chunk of glacial ice is left behind as a glacier recedes the ice itself could create a depression and melt to fill it, creating a “kettle lake”. Kettle lakes are irregularly shaped in the manner of the original ice blocks that produced them2. Kettle lakes are also sometimes referred to as pothole lakes.
Glaciers and ice can create lakes in other unique ways. Periglacial lakes form when ice shapes part of a lake’s margins, restricting otherwise natural drainage of the landscape. Some lakes, such as Lake Vostok in Antarctica, are known as subglacial lakes because they are covered by a perennial ice sheet on their surfaces. Fjord lakes can also form from the action of glaciers carving steep fjord valleys and depositing rocks, boulders, and soils — moraine — at one end of the valley, forming a lake.
Another significant lake-forming force is movement of the tectonic plates that form the Earth’s crust. These lakes typically form at fault lines where plates meet and earthquakes are more common. When adjacent plates separate at fault lines, the steep, narrow gap between them can result in the formation of a graben. Some of the largest, deepest, and oldest lakes on Earth are graben lakes, where a long history and large size can host unique biological diversity. Perhaps the most famous graben lakes are Lake Baikal and the African rift valley lakes, including Lake Tanganyika. Lake Baikal, located in eastern Russia is the world’s oldest, deepest, and largest lake (by volume). Lakes may also occur at points of tectonic upwarping, where the edges tilt or rise to form a discontinuity in the landscape. These tectonic lakes are typically not as deep as graben lakes2.
Indirectly controlled by tectonic activity, volcanism can also create lakes. Ejected magma may leave behind a fissure that holds water in what is termed a maar lake. When the roof of a volcanic crater caves in, a larger caldera may form a crater lake, such as the aptly named Crater Lake in Oregon, U.S.A. Both kinds of lakes are typically deep in relation to surface area, and drain a limited area. High concentration of volcanic minerals and few nutrients typically yield little productivity in these lakes, which means they are typically clear and deep blue in color.
Many lakes result from river movements of sediments that slowly create lakes over time. The force of water rushing along a riverine flowpath can be tremendous and lead to extensive erosion. Over time, eroded areas may become lake basins. When a lake forms at the foot of a waterfall, it is referred to as a plunge-pool lake.
As riverine erosion occurs, sediments are collected and deposited downstream in the process. Large rivers can deposit sediments in a manner that dams tributary streams and allows new lakes form as a result., These lakes are called lateral lakes. At river bends, turbulence and sediment deposition can build up. Occasionally, this sediment causes the river path to divide and may actually dam of a portion of the river bend entirely. The resulting water body is called an oxbow lake2.
Lakes may form on river floodplains when depressions in the floodplain remain filled as floodwaters recede. These lakes are called lateral levees or dish lakes when the ratio of length to width is less than five, or channel lakes when the ratio of length to width is greater than five. The billabongs of Australia are examples of lateral levee lakes2.
Lakes can also form at the mouths of rivers and on deltas. Lakes here form in a similar fashion as Oxbow Lakes, with the aggregation of sediments on a delta closing off otherwise natural water flow. These lakes are referred to as fluviatile lakes or alluvial fan dam lakes. Often, these lakes may be young in origin and disappear with floods and higher water flow.
Reservoirs and impoundments are man-made lakes that form through intentional or unintentional damming or other processes that lead to the pooling of water in one location. Examples include reservoirs that are constructed for drink water, power generation, fisheries, or other recreational activities.
Other types of man-made lakes include farm ponds, ornamental lakes, and quarry lakes, which form in quarry pits used to extract minerals and other resources.
Natural reservoirs can form from the activities of animals and plants such as beavers. Beavers often dam rivers, forming lake behind the dam. Given enough time, sediments can aggregate against the dam, forming a levee and a natural reservoir.
Erosive forces have the power to form other types of lakes. The action of waves along ocean shoreline can also lead to lake formation through erosion and damming of estuaries and river deltas. These lakes may be semi-saline brackish water lakes.
The force of wind is also capable of creating lake basins in coastal regions at the boundaries of large lakes by manipulating sand dunes to create temporary depressions where precipitation collects. Wind blowing across geographically flat regions can move or erode soil sufficiently that shallow lakes called deflation basins or playas result. Often these shallow lakes are endorheic, meaning they don’t drain to the ocean but instead only lose water through evaporation or seepage.
Certain bedrocks, particularly limestone, are easily eroded by even slightly acidic water and may dissolve to form lakes called solution lakes, cenotes, sinkholes, or karsts. Solution lakes may occur on the surface or below ground in caves; they are typically highly circular due to the even chemical erosion of the bedrock at their edges2.
Lakes in polar latitudes may result from freeze/thaw cycles. The action of permafrost in the Arctic causes raised, polygonal soil mounds in which water collects to form cryogenic lakes. When these ponds connect, or an area of permafrost melts, a larger thermokarst lake results. Interestingly, cryogenic and thermokarst lakes are becoming more common, probably as a result of global climate change and the consequent warming of the arctic.
- Larson, G & Schaetzl, R. (2001) Origin and evolution of the Great Lakes. J. Great Lakes Res. 27(4), 518–546.
- Wetzel, Robert G. (2001). Limnology, 3rd ed. San Diego: Elsevier.
- Wayne Wurtsbaugh. American Society for Limnology and Oceanography online photo registry. 2010. Retrieved online at: http://www.aslo.org/photopost/showphoto.php/photo/625/title/cirque-lakechina-lakeidaho-/cat/502
- Midendian. Kettle lakes in the meadow below Fitz Roy, Santa Cruz, Argentina. 2010. Retrieved online at: http://www.flickr.com/photos/midendian/3448102248/
- Goldman, E. (2003). Puzzling over the origin of species in the depths of the oldest lakes. Science, 299, 654-655.
- LivingWilderness.com. Palouse Falls, Eastern Washington. 2010. Retrieved online at: http://www.flickr.com/photos/livingwilderness/160207750/
- Wickens, H. Summer Tour of Borneo. 2003. Retrieved online from: http://homepage.ntlworld.com/harry.wickens/borneo/borneo-3.htm
- Adams, A. 1941. Boulder Dam.
- Open University Geological Society Mainland Europe. Thermokarst lakes. 2010. Retrieved online at: http://ougseurope.org/rockon/surface/thermokarst.asp
Lakes can vary in three dimensions: length, width, and depth. The shape and volume of a lake, referred to as lake morphology, often relates to a lake’s age, origins, chemical makeup, and the organisms that live within it. Lake shape is influenced by the surrounding landscape and controls much of what goes on physically and biologically underwater. For example, when lakes have many small inlets and bays, these areas can warm up quickly and are not affected by winds that can pick up speed over the large open area of a typical lake body.
The length of a lake is measured as the longest straight-line shoreline-to-shoreline distance across a lake. Often, the length is an important factor regulating the local weather climate. Winds can pick up speed over open water, which is much smoother than the surrounding landscape. The length of a lake is also called the fetch, which is a term that describes the longest distance an air mass can travel across a lake (Figure 1). In most lakes, the fetch determines the size of waves and how deeply warm surface waters are mixed. Wind travelling over a long fetch is able to cause significant mixing in a shallow lake1. Its estimated that a fetch greater than about 60 miles (100 km) is required to generate lake-effect snow2.
Another important measurement is lake width (“W” in Figure 1), taken as the longest shoreline-to-shoreline measurement at right angles to the length. Common lake shape measurements other than length (fetch) and width include the maximum depth, the average depth, and the relative depth, which is a ratio of the maximum depth the to the lake’s diameter. Typically, the maximum depth of the lake can be found at roughly central location or at some distance from the shoreline. Most lakes have an average depth of about 10 meters. Depth can frequently predict the productivity of the lake, or how much photosynthesis it fosters, since a shallow lake will have greater exposure to both sunlight and nutrients3.
The shape of a lake’s shoreline is strongly connected to lake biology. The characteristics of the shoreline — whether it is jagged or smooth, curved or angular — affect what happens underwater. The more jagged and indented the shoreline, the more the lake is affected by inputs from the surrounding land through runoff or groundwater leaching3. Many organisms depend on natural, unaltered lake shorelines for shelter and nesting sites. Often, home owners who live along lakes remove debris and vegetation to clean up the lake shoreline, but doing so can hurt underwater organisms, including larval fish and amphibians. Trees and branches that fall into the water, referred to as coarse woody debris, are important shelters and nest sites for many creatures, including fish and their invertebrate prey. Also, as wood and plant debris decompose, they release many important dissolved nutrients that will feed plants and microorganisms4.
Most lakes are roughly circular, but some lakes can be highly irregular in shape. Compare these two lakes in Figure 2.
Littoral Zones and Pelagic Zones
Lake scientists classify the areas of an individual lake based on gradients of depth that increase away from the shoreline. The shallow perimeter of the lake is typically referred to as littoral. Littoral zones are shallow enough that sunlight is able to penetrate to the sediments and support photosynthetic plants. Areas where attached aquatic vegetation (called macrophytes) can be seen emerging from the water are typically littoral. The depth of the littoral zone can depend on the transparency of the water, where vegetation can grow in deeper areas when a lake is more transparent.
The open water of the lake is referred to as the pelagic zone. Here, photosynthesis and primary production is dominated by phytoplankton which can remain suspended in the water column3.
Want to experience what it feels like to fly through a lake underwater? Scientists and lake managers often measure the underlying shape of a lake — termed bathymetry — with sophisticated sonar equipment. Lake Tahoe, the second deepest lake in the U.S., has detailed movies highlighting the lake’s bathymetry7.
- Hall, S.R & Rudstam, L.G. 1999. Habitat use and recruitment: a comparison of long-term recruitment patterns among fish species in a shallow eutrophic lake, Oneida Lake, NY, U.S.A. Hydrobiologia 408/409,101–113.
- Wikipedia. Lake Effect Snow. 2010. Retrieved online at: http://en.wikipedia.org/wiki/Lake-effect_snow#Fetch
- Wetzel, Robert G. 2001. Limnology, 3rd ed. San Diego: Elsevier.
- Christensen, D. L., et al. 1996. Impacts of lakeshore residential development on coarse woody debris in north temperate lakes. Ecological Applications, 6 (4), 1143-1149.
- The Water Line. Reservoirs vs. Lakes. 2003. Retrieved online at: http://www.lmvp.org/Waterline/winter2003/dam.htm
- New Zealand Ministry for Water and the Environment. 2010. Draft Guidelines for the Selection of Methods to Determine Ecological Flows and Water Levels. Retrived online at: http://www.mfe.govt.nz/publications/water/draft-guidelines-ecological-flows-mar08/html/
- U.S. Geological Survey. 2010. Lake Tahoe Data Clearinghouse. Retrieved online at: http://tahoe.usgs.gov/movies.html
Kevin Rose | Miami University
Why are lakes different colors?
Lakes exist in many sizes and shapes, but often the most obvious characteristic of a lake is its color (Figure 1). The differences in color or transparency between lakes can be rather striking, but even for a single lake, color changes can occur over time. The color of lake can tell you many things about the water body (e.g., including nutrient load, algal growth, and water quality) and also about the surrounding landscape.
There are three main categories of lake color: blue water lakes, green water lakes and brown water lakes. Lake color and clarity can measured using a Secchi disk or underwater light sensors such as a LiCor PAR sensor.
Blue water lakes
Blue water lakes contain low concentrations of algae and other substances, resulting in high clarity and a deep blue color. Water molecules absorb longer, visible wavelengths (e.g. red light, 600-700 nm) while shorter, blue wavelengths (< 500 nm) pass deeper into the water column. These short wavelengths scatter to create a deep blue color in clear lakes. Blue lakes are common in areas with fast draining soils and small lake watersheds. These lakes usually have very low algal growth, supporting few fish unless the lakes are stocked. The deep blue color of some lakes is a testament to the pristine character of the water and low human impact in the surrounding watershed. These high quality bodies of water are often the focus of local conservation efforts.
Green water lakes
Green water lakes commonly have high concentrations of chlorophyll-containing algae which can give water a green color. Chlorophyll can be measured with sensors such as the YSI chlorophyll probe. Green lakes are often eutrophic and typically contain more harmful algal blooms than other types of lakes. Activities such as farming or septic system failure can increase the green color of lakes through nutrient inputs which act as a fertilizer for algae. The high productivity of green lakes usually enables them to support more fish, but the poor water quality conditions can depress dissolved oxygen levels in hot summer months; these conditions can cause fish kills where oxygen drops too low for fish to survive.
Brown water lakes
Brown water lakes contain high amounts of tea-like substances, known as dissolved organic matter. Typically, brown lakes are surrounded by forests or wetlands. Dense forests provide dark organic material that dissolves in lake water like a teabag. This dissolved organic material stains the water brown and shades the underwater world.
Overall, brown water lakes tend to be light-limited. The algae in these lakes survive through certain adaptations that allow them to adjust to low light levels. These lakes can also sometimes be acidic and contain few fish or other organisms.
Can lakes change color?
Both natural and human activities can cause changes in lake color and clarity. The development of communities or the use of agricultural fertilizers around lakes often reduces water clarity and adds nutrients, shifting lakes from blue water to green water. Lakes can also naturally become more eutrophic and green over time. As lakes age over centuries, nutrients, sediment and plant material slowly build up. This natural process is much slower than changes caused by human impacts.
While human impacts often change lakes from blue to green, conservation and protection can improve the clarity and color of lakes. In areas where water quality has been degraded by pollution, eutrophication, or changes in land use, community action to improve water quality through enhanced laws and zoning can improve water quality and shift lakes from green water to blue water. This process is often difficult, however, as lakes tend to remain in the color state in which they currently exist.
Seasonally, lakes can change in color. In many lakes, rapid algal growth in the spring months produces a green color. However, this period is usually followed by a clear water phase (i.e., blue water lake) as zooplankton emerge and consume algae. The length of clear water phases can vary and is determined by the ecological interactions among aquatic organisms. In addition, sunlight can bleach organic matter in the same way that materials left outside for too long become bleached and faded. The bleaching typically follows day length and lakes can be most transparent (e.g. most blue in color) when the most bleaching occurs around the summer solstice.
- Kalff, J., 2002. Limnology, New York.
- Stolzenbach, K.D. Atmospheric Deposition: Figure 3: An eutrophic lake choked by an algae bloom. Retrieved online May 2010 at: http://www.ioe.ucla.edu/reportcard/article.asp?parentid=1497
- NH Division of Forest and Lands. Acidic brownwater lake/pond. Retrieved online May 2010 at: http://www.nhdfl.org/about-forests-and-lands/bureaus/natural-heritage-bureau/photo-index/acidic-brownwater-lake-pond.aspx
- Greeson 1969. Lake eutrophication – A natural process. JAWRA.
- Jeppesen, Jensen, Søndergaard and Lauridsen. 1999. Trophic dynamics in turbid and clearwater lakes with special emphasis on the role of zooplankton for water clarity. Hydrobiologia 408/409:217–231
- Tõnno, Kunnap and Noges. 2003. The role of zooplankton grazing in the formation of ‘clear water phase’ in a shallow charophyte-dominated lake. Hydrobiologia 506:353–358
- Morris and Hargreaves. 1997. The Role of Photochemical Degradation of Dissolved Organic Carbon in Regulating the UV Transparency of Three Lakes on the Pocono Plateau. Limnology and Oceanography 42: 239-249.
Where Are Lakes?
Dave Davis | Kent State University
For many people, lakes are a part of daily life that are taken for granted. They are often viewed as commodities: sources of water for drinking and farming, food, and recreation. Lakes are valued for their aesthetics as well, as shown by the high cost of lakefront properties. While many have gone fishing on a lake in the countryside or hiked out to an alpine lake in the mountains on vacation, it’s important to note lakes aren’t everywhere. In fact, some places don’t have many lakes at all. Where are lakes — and why are they where they are?
Lakes occupy only a small percentage of Earth’s total surface area. Recent studies estimate the total surface area of lakes at about 4,200,000 km2 — only about 2.8% of the planet’s land surface area (or less than 1% of the Earth’s total surface area)1. It is thought that large lakes such as the Great Lakes of the U.S. and Canada make up a large portion of this total, although small lakes (<0.1 km2) do not commonly appear on maps and may not be counted in typical surveys1. Lakes and other freshwaters range in size from 0.001 km2 for the smallest lakes and ponds, and the largest, the Caspian Sea, at 378,119 km1, 2. Although a few extremely large lakes may dominate area, small lakes dominate the total number of lakes around the world. Lakes of all sizes are an important area of biological study, because while lakes only make a small contribution to the total surface of the planet, they proportionally make a much larger contribution, compared to other environments, to ecological processes such as carbon cycling2 and biodiversity.
Based on data collected on lake size distribution, it is estimated there are over 304 million lakes in the world1. Lakes are generally found in specific regions depending on the geology and geography of that area4. Lakes occur in these specific regions typically because of how they form. To support lakes, a region must have depressions in the ground capable of holding water and enough rainfall to sustain the lake’s water supply by balancing evaporation and other losses. The total rainfall in an area correlates strongly to the number of lakes and ponds present; hence, dry areas have fewer lakes1. Additionally, many lakes are manmade (these are also called reservoirs or impoundments). These lakes are typically built for specific purposes, such as water supplies for metropolitan areas or agricultural irrigation and are found near cities or farms. Man-made lakes are quite important both to humans and to other organisms, as their establishment has major effects on aquatic life3.
Using modeling techniques, limnologists have been able to calculate lake distributions for various regions of the world, using lakes of surface area 1-10 km2 as a model1. This data had led to the discovery of some continental trends in lake distribution. In North America, lake distribution tends to be highest in the eastern United States and Canada. Central American countries as well as the northwestern regions of Canada and the United States are also relatively dense with lakes, but the central United States and Mexico have the smallest lake density. South America shows trends of high lake densities in its northeastern and central-eastern regions, but the southern and western regions of the continent have few lakes. Europe shows a fairly uniform distribution, ranging from 601-1000 lakes per 1,000,000 km2, but shows a high density along the northern and southern regions of western Europe. Africa shows few lakes in its northern and southern regions, but possesses a much higher lake density in its central regions. In Asia, much of the lake density is within Russia, southern China, Japan, India, and other surrounding countries. Finally, Australia shows a low distribution of lakes throughout, with the only exceptions being coastal regions of Australia and Papua New Guinea1.
- Downing, J. A. et al. 2006. The global abundance and size distribution of lakes, ponds, and impoundments. Limnology and Oceanography, 51(5), 2388-2397.
- Hanson, P.C. et. al. 2007. Small lakes dominate a random sample of regional lake characteristics. Freshwater Biology, 52, 814-822.
- Smith, S.C. et. al. 2002. Distribution and significance of small, artificial water bodies across the United States landscape. The Science of the Total Environment, 299, 21-36.
- Riera, J.L. et. al. 2000. A geomorphic template for the analysis of lake districts applied to the Northern Highland Lake District, Wisconsin, U.S.A. Freshwater Biology, 43, 301-318.