Water level ups and downs may be an emotional roller coaster ride for some lakefront property owners. It can be alarming to see your pier extending into dry lakebed or your shoreline submerged by flooding.
In order to understand the cause of lake level variations, one must calculate the “water budget” of a lake. Similar to balancing your checkbook, a water budget does an accounting of all the inputs and outputs of water to a lake. Any imbalance results in a change in lake level.
When water levels drop because of human reasons—such as groundwater removal—there can be long term effects that can be devastating to an ecosystem. However, water level fluctuations are also a part of natural cycle, and temporarily lower water levels can benefit the lake. Factors that influence lake water levels include the source of a lake's water (lake type), the depth of the lake, precipitation and evaporation, over pumping of groundwater, and the amount of impervious surfaces within the lake's watershed.
Human Caused Water Level Declines
Water level declines can be caused by human activity. Most of Wisconsin's lakes receive all or part of their water from groundwater. Over pumping of groundwater for industry, agricultural, and municipal uses combined with increasing amounts of impervious surfaces over larger watershed areas has resulted in dramatic declines in groundwater levels.
In some areas of the state, lake levels have dropped because high capacity wells have reduced or stopped inflow of groundwater into the lake. In areas where groundwater demand and use exceed sustainable rates, slowing or stoppage of the natural discharge of groundwater into lakes and other surface waters has reduced critical supplies of surface water for fish and other wildlife, especially during dry periods.
High capacity wells pump 100,000 gallons per day or more (with some pumping up to 1 to 2 million gallons per day). Whether these wells are located near or far away from the lake, they can dramatically influence the groundwater flow through the lake, lake water levels, and can impact water quality, lake ecosystems, and recreational uses.
Impacts of high capacity well operation on a lake are determined by the hydrogeology of the region surrounding the lake and the well site. Site-specific analyses are required to determine specific impacts on individual lakes.
As watersheds are developed, the amount area of area covered by impervious surfaces (roads, driveways, rooftops, etc.) increases. This prevents precipitation from infiltrating into the ground and recharging groundwater aquifers. Having less water in aquifers can lessen the flow of groundwater into lakes and other surface waters.
To learn more, check out these fact sheets:
Natural Fluctuations in Water Levels
Natural fluctuations in lake water levels can result if less rain occurs, there is less runoff from snow, more water evaporates from the lake, or a combination of all of these factors over time. Depending on the depth of the lake, water level fluctuations may be dramatic, or barely noticeable.
Especially in shallow lakes, water level fluctuations can be part of a natural and normal cycle. This process of fluctuating water levels has been happening for thousands of years. Many plants and animals—like bulrushes—have evolved around this natural phenomenon, and depend on it.
One of the most beneficial lake responses to lower water levels is the germination of plants on exposed sediments. When water retreats from shore, old dormant seedbeds are exposed to the elements, triggering many species into activity. The picture below shows where the Ordinary High Water Mark (OHWM) usually is, the retreating lake level from the year's 2003 and 2002, and the plants that have grown in the exposed lake bed during the lower water level period.
These plants start to sprout in the new shoreline, providing food and habitat for wildlife, and creating a filtration system for the lake. When water levels rise back up—which they will—the plants that grew on the formerly exposed lake bed will either succumb or become part of the aquascape. Bulrushes are an excellent example of a species that benefits from fluctuating water levels. Bulrushes like the occasional dry spell to regenerate new plants. They can survive in flooded areas for many years, providing habitat for fish and wildlife and purifying water. When water levels return, these plants will remain.
In extreme cases of water level decline, you might start to see small trees such as aspen, willow or even jack pine start to grow on lakebeds. These trees will die out when the water returns, so removal is not necessary. The plants that succumb to flooding waters become instant habitat and food for many organisms, including young game fish.
What about some of the other critters? What about the muskrats, fish, ducks dragonflies, and all the other things that make our lake experience what it is? They too have evolved to live with the natural ups and downs and do absolutely fine. They follow the slow decline in water levels and adjust accordingly.
When lake water levels are low, lake users may have to adjust their activities. Boaters may have to operate their motors in deeper water so that propwash does not churn up lakebed sediments (which can cloud the water and release nutrients like phosphorus into the water) and wave action does not erode the shoreline. Property owners can welcome the native plants sprouting in newly dried lakebed as a natural process, and not eliminate these plants by "cleaning" the shoreline. To learn more, click here (exits to DNR Lakes web site).