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For information on Wisconsin's natural communities, contact:
Ryan O'Connor
Natural Heritage Inventory Ecologist

Inland lakes (group)


General natural community overview

Inland lakes are naturally occurring bodies of standing water with a huge 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 the physical and chemical characteristics of any given lake.

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 >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 and meromictic lakes, and spring ponds are defined 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. In stratified lakes (typically deeper lakes), a thermocline develops during the summer and winter. In the spring and fall, this zone of marked temperature difference breaks down, allowing for the mixing of bottom and surface waters and a 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 the purposes of 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 equals or exceeds 50 ppm and are less susceptible to acidification because they have a high concentration of hydroxyl, carbonate, and/or bicarbonate ions, which buffer acids. Soft water lakes have a total alkalinity of less than 50 ppm and have low capacity to buffer acids.
  • Water Source -- Drainage, Seepage, or Spring. Drainage lakes have both an inlet and outlet, and the main 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 to be artificial lakes or impoundments. Seepage lakes do not have an inlet or an outlet, and only occasionally overflow. As landlocked waterbodies, the principal source of water 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 fairly common type of lake in northern Wisconsin.

Wisconsin Wildlife Action Plan Inland Lake Type Information:

Inland Lake Name WI Clean Water Act Name Stratification Hydrology
Small Lake--hard, bog Small Lakes Variable Any Hydrology
Small Lake--soft, bog Small Lakes Variable Any Hydrology
Small Lake--meromictic Small Lakes Variable Any Hydrology
Small Lake--other Small Lakes Variable Any Hydrology
Large Lake--shallow, hard and very hard (marl), drainage Shallow headwater mixed headwater drainage
Large Lake--shallow, hard and very hard (marl), drainage Shallow lowland mixed lowland drainage
Large Lake--shallow, hard, seepage Shallow seepage mixed headwater drainage
Large Lake--shallow, soft, drainage Shallow headwater mixed headwater drainage
Large Lake--shallow, soft, drainage Shallow lowland mixed lowland drainage
Large Lake--shallow, soft, seepage Shallow seepage mixed headwater drainage
Large Lake--deep, hard, drainage Deep headwater stratified headwater drainage
Large Lake--deep, hard, drainage Deep lowland stratified lowland drainage
Large Lake--deep, hard, seepage Deep seepage stratified seepage
Large Lake--deep, soft and very soft, seepage Deep seepage stratified seepage
Large Lake--deep, soft, drainage Deep headwater stratified headwater drainage
Large Lake--deep, soft, drainage Deep lowland stratified lowland drainage
Riverine Impoundment Impounded flowing waters variable headwater or lowland drainage
Riverine Lake - Pond lowland drainage

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 there is considerable overlap. Where the two communities do 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, greatly affects the types and abundance of aquatic plants present.

Aquatic plants, including both emergent and submergent aquatic vegetation, form the foundation of healthy and flourishing aquatic ecosystems - both 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 own 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 current. Aquatic plants also serve as spawning habitat for fish and amphibians, and support populations of aquatic insects that serve as a food base for other species.


Wisconsin Wildlife Action Plan graphic

What are conservation actions?

Conservation actions respond to issues or threats, which adversely affect species of greatest conservation need (SGCN) or their habitats. Besides actions such as restoring wetlands or planting resilient tree species in northern communities, research, surveys and monitoring are also among conservation actions described in the WWAP because lack of information can threaten our ability to successfully preserve and care for natural resources.

Threats/issues and conservations actions for natural communities




Aurora Lake, an undeveloped, shallow, softwater drainage lake, supports extensive beds of aquatic macrophytes.

Photo by Thomas Meyer.


Seepage Lake, Langlade County.

Photo by Emmet Judziewicz.


Two very different seepage lakes. In the foreground is a shallow, muck-bottomed lake, bordered by boggy wetlands. Back lake is deep, with a firm bottom, and upland shoreline.

Photo by Eric Epstein.


Drainage lake. Border of Ashland Co.

Photo by Eric Epstein.


Aerial view of Lake Alva, a deep, soft, seepage lake that is the centerpiece of an outstanding natural features complex.

Photo by Eric Epstein.

Note: photos are provided to illustrate various examples of natural community types. A single photograph cannot represent the range of variability inherent in a given community type. Some of these photos explicitly illustrate unusual and distinctive community variants. The community photo galleries are a work in progress that we will expand and improve in the future.

Last revised: Tuesday, August 30, 2022