Aquatic Communities

The tables below compare natural aquatic communities used in the 2025-2015 Wisconsin Wildlife Action Plan with those used by the DNR's Natural Heritage Inventory and River and Lakes programs.

Springs, Streams and Rivers

Lakes

Inland Lakes Description

Inland lakes are naturally occurring bodies of standing water with considerable diversity in size, configuration, water chemistry, and biota. Glaciation, post-glacial water flow, soil characteristics, topography, bedrock composition, land cover, land use, and other factors can all combine to determine any given lake's physical and chemical characteristics. In Wisconsin's Wildlife Action Plan, "Inland Lakes" were divided into multiple inland lake types reflective of their hydrology, depth, alkalinity, and landscape position using the following four characteristics:

• Size -- Small or Large. Small lakes are typically <10 acres and large lakes are>10 acres. There are thousands of small lakes (<10 acres) across the state. They can exhibit diverse hydrological regimes, depths, substrates, alkalinity, and associated species. Small bog, meromictic lakes, and spring ponds are defined as small lake types.
• Water Depth -- Deep or Shallow. Depth is just one of several lake characteristics that influence stratification; others include surface area, water source, and water clarity. Stratification refers to variations in temperature at different depths of a lake throughout the seasons. A thermocline develops during the summer and winter in stratified lakes (typically deeper lakes). In the spring and fall, this zone of marked temperature difference breaks down, allowing for the mixing of bottom and surface waters and the redistribution of oxygen and nutrients. Lakes that do not stratify thermally (typically shallow lakes) can become oxygen depleted as the water warms and decomposition exceeds primary production. This can also occur during the winter when ice and snow cover the surface, inhibiting photosynthesis--"freezeout" conditions may then prevail. For this classification, associated plant and fish species are correlated with deep (> 18 feet) and shallow (< 18 feet) water.
• Alkalinity -- Hard or Soft. Hard water lakes have a total alkalinity that equals or exceeds 50 ppm. They are less susceptible to acidification because they have a high concentration of hydroxyl, carbonate, and bicarbonate ions, which buffer acids. Softwater lakes have a total alkalinity of less than 50 ppm and have a low capacity to buffer acids.
• Water Source -- Drainage, Seepage, or Spring. Drainage lakes have both an inlet and an outlet, and the primary water source is from streams. Most major rivers in Wisconsin have drainage lakes along their course. Drainage lakes owing one-half of their maximum depth to a dam are considered artificial lakes or impoundments. Seepage lakes do not have an inlet or an outlet and only occasionally overflow. As landlocked waterbodies, the principal water source is precipitation or runoff, supplemented by groundwater from the immediate drainage area. Since seepage lakes commonly reflect groundwater levels and rainfall patterns, water levels may fluctuate seasonally. Seepage lakes are the most common lake type in Wisconsin. Spring lakes have no inlet but do have an outlet. The primary source of water for spring lakes is groundwater flowing into the bottom of the lake from inside and outside the immediate surface drainage area. Spring lakes are the headwaters of many streams and are a relatively common type of lake in northern Wisconsin.

Plant communities associated with inland lakes can fall into two general categories: submergent marsh and floating-leaved aquatic, and both communities can be found within a single lake. Submergent aquatic macrophytes tend to occur in deeper water than beds of floating-leaved or emergent species, but considerable overlap exists. Where the two communities co-occur, the large-leaved pond lilies, when dominant, can inhibit the development of submergent or emergent plants by casting heavy shade over the plants below. The water clarity, chemistry, substrate, and stratification at a given lake affect these two plant communities. The water chemistry, perhaps more so than other ecological factors, dramatically affects the types and abundance of aquatic plants.

Aquatic plants, including emergent and submergent aquatic vegetation, form the foundation of healthy and flourishing aquatic ecosystems - within lakes and on the shores and wetlands surrounding them. They not only protect water quality but also produce life-giving oxygen. Aquatic plants are a lake's filtering system, helping to clarify the water by absorbing nutrients like phosphorus and nitrogen that could stimulate algal blooms. Plant beds stabilize soft lake bottoms and reduce shoreline erosion by reducing the effect of waves and currents. Aquatic plants also serve as spawning habitats for fish and amphibians and support populations of aquatic insects that serve as a food base for other species.

Great Lakes Information

Lake Michigan is among the world's most significant and deepest freshwater lakes. This massive waterbody covers 22,300 square miles and has 407 miles of coastline in Wisconsin. The lake is primarily cold water with summer maximum water temperatures below 22 degrees Celsius (72 degrees Fahrenheit). Lake Michigan is relatively infertile but warmer and more fertile than Lake Superior. Historically, the fish fauna consisted primarily of lake trout, ciscoes/whitefishes, and sculpins. Warmer and more fertile harbors and bays (e.g., Green Bay) had a more diverse assemblage of cool and warm water fishes, especially in the Perch family. Invasion by the sea lamprey due to commercial alterations of the Great Lakes waterways led to the first large-scale disruption of the biotic community, significantly depleting the native lake trout population. By the 1970s, three cisco species and three others extirpated from Lake Michigan were extinct. Only Lake Superior supports populations of two of these extirpated species, and only Lake Huron supports the third. Over-harvest and other factors caused a steep decline in the population of lake herring. Now the biota is dominated by introduced or invasive non-native species, including Pacific salmon and trout, alewife, rainbow smelt, ruffe, white perch, gobies, zebra and quagga mussels, and exotic zooplankton.

Lake Superior is a unique and vast resource of fresh water covering 31,700 square miles. It is the largest freshwater lake in the world by surface area and has 156 miles of coastline in Wisconsin. The lake is primarily cold water with summer maximum water temperatures below 22 degrees Celsius (72 degrees Fahrenheit). Lake Superior is relatively infertile with a historic fish fauna that consists primarily of lake trout, ciscoes/whitefishes, and sculpins. Warmer and more fertile harbors and bays (e.g., Chequamegon) had a more diverse assemblage of cool and warm water fishes, especially in the Perch family. Now the biota is dominated by introduced or invasive non-native species. Due to extirpations in other lakes, Lake Superior supports the last remaining Great Lakes population of two whitefish relatives - kiyi and short jaw cisco. Lake Superior has not experienced the same development, urbanization, and pollution levels as the other Great Lakes. Although Lake Superior is the cleanest and most healthy of all the Great Lakes, it is still threatened by toxic pollutants that bioaccumulate in the food chain and persist in the environment. These substances can be transported long distances in the atmosphere and end up in the lake. Local sources contribute pollutants to air and water, adding to the pollutant load entering Lake Superior. Because of its long retention time (191 years), pollutants entering Lake Superior can remain in the lake for over a century before draining to the lower Great Lakes.

Visit the Office of the Great Lakes to learn more.

Associated Rare Species and Ecological Landscapes

Species of Greatest Conservation Need (SGCN) are associated with habitats (or natural communities) and places on the landscape. Understanding relationships among SGCN, natural communities and ecological landscapes help us decide on issues affecting SGCN and their habitat and how to respond. Download the Wildlife Action Plan association score spreadsheet to explore rare species and ecological landscapes associated with these natural aquatic communities.

Additional Aquatic Natural Community Descriptions:

• Ecological Landscapes of Wisconsin Chapter 7 - Aquatic Features
• Wisconsin Natural Heritage Inventory
• DNR River and Lakes