Definition

General natural community overview

Inland lakes are naturally occurring bodies of standing water with a huge diversity in size, configuration, water chemistry, and biota. Their surface area can range from less than one acre to over 137,000 acres and their depth can range from less than a foot to more than 230 feet. 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. The concentration of glacial kettle lakes within the Northern Highlands Ecological Landscape is globally important. Some of the lake types there are rare, and support many rare organisms.

Natural lakes in Wisconsin frequently are classified by the source of water supply. Based on water source and outflows, four categories of lakes are commonly recognized:

•Drainage lakes – These lakes have both an inlet and outlet where the main water source is stream drainage. 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 (see Section 3.3.1.3 for information regarding impoundments/reservoirs).

•Seepage lakes – These 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 – These 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.

•Drained lakes – These lakes have no inlet, but like spring lakes, have a continuously flowing outlet. Drained lakes are not groundwater-fed. Their primary source of water is from precipitation and direct drainage from the surrounding land. Frequently, the water levels in drained lakes will fluctuate depending on the supply of water. Under severe conditions, the outlets from drained lakes may become intermittent. Drained lakes are the least common lake type found in Wisconsin.

Lakes vary based on physical characteristics, such as size, depth, configuration, chemical characteristics (such as soft versus hard water), water clarity, or the types of plant and animal life present. For example, Some lakes are almost perfectly round in shape whereas others are highly convoluted. Hard water lakes have higher levels of dissolved minerals such as calcium, iron and magnesium than soft water lakes. Some lakes, especially those near acidic wetlands such as bogs, are stained with tannic acid that leaches from surrounding vegetation. The water in these "tannin lakes" may range in color from a dark brown "coffee" color to light brown.

These waterbodies also vary greatly in fertility and clarity, with clearer, lower fertility lakes more common in northern Wisconsin. Large, fertile, southern Wisconsin lakes with stream inlets and outlets generally have the greatest variety of species. Most lakes are dominated by cool and warmwater fishes, particularly the family Centrarchidae (sunfishes).

Rare animals

Species of Greatest Conservation Need

The following Species of Greatest Conservation Need are listed according to their level of association with the natural community type, based on the findings in the Wisconsin Wildlife Action Plan.

Please see the Wildlife Action Plan, Chapter 2.4 to learn how this information was developed.

Opportunities

Management Opportunities

The following Ecological Landscapes have the best opportunities to manage for , based on the Ecological Landscapes of Wisconsin Handbook.

Major
A major opportunity for sustaining the natural community in the Ecological Landscape exists, either because many significant occurrences of the natural community have been recorded in the landscape or major restoration activities are likely to be successful maintaining the community's composition, structure, and ecological function over a longer period of time.

Important
Although the natural community does not occur extensively or commonly in the Ecological Landscape, one to several occurrences do occur and are important in sustaining the community in the state. In some cases, important opportunities may exist because the natural community may be restricted to just one or a few Ecological Landscapes within the state and there may be a lack of opportunities elsewhere.

Present
The natural community occurs in the Ecological Landscape, but better management opportunities appear to exist in other parts of the state.

Threats / Actions

These threats and priority conservation actions were identified for the community type in Wisconsin, and they apply to all of Wisconsin's Ecological Landscapes unless otherwise indicated. Please see the Wisconsin Wildlife Action Plan, Chapter 3.3 , for more information

Threats

• Changing land use practices and resulting non-point source pollution from urban and agricultural runoff and other sources are leading to habitat loss, eutrophication, and increases in salinity.
• Shoreline and littoral-zone alteration and development, as well as shallow-water motorized recreation, are degrading lake habitat.
• Mercury bioaccumulation in fish poses a health risk to humans and other animals that eat fish, especially in waters with sediments that increase the rate of mercury methylization.
• Exotic invasive plant and animal species (e.g., common carp, rainbow smelt, zebra mussel, rusty crayfish, Eurasian water-milfoil, curly pondweed, flowering rush) are degrading habitats, altering food webs and species interactions, and displacing native species. Other exotics, such as the parasite Heterosporis sp., are spreading to lakes across northeast Wisconsin, infecting yellow perch and other species.

Conservation actions

• Improve watershed and riparian land-use practices to reduce non-point source pollution.
• Protect and restore shoreline and littoral-zone habitat. Support shoreline research, education, and restoration conducted by lake districts, UW-Extension and other institutions, restoration consultants, and others.
• Improve regulations and education regarding actions such as boat cleaning and disinfection to prevent the introduction of additional exotic species and slow the spread of existing populations of invasive species.
• Continue to seek statewide and regional reductions in mercury emissions from key sources.

Photos

Click to view a larger version. Please considering donating your photos to the Endangered Resources Program for educational uses. Photo use

Photos

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.