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Where lake water comes from determines how to protect quality

Lakes behave differently depending on their water source and type of outflow. The source of a lake's water supply is very important in determining its water quality and in choosing management practices to protect that quality.

There are three main types of natural lakes based on water flow. First, a seepage lake is a natural lake that has no inlets or outlets. A seepage lake is fed by precipitation, limited runoff and groundwater. Since there is no inlet in a seepage lake, phosphorus sources to the lake are mainly from practices occurring directly around the lakeshore such as septic systems and runoff from lawns. Protecting groundwater is also very important in seepage lakes since that is the main water source for the lake.

The second type of lake is a groundwater drainage lake. This type of lake has no inlets, but has a stream outlet. An example of a groundwater drainage lake near Detroit Lakes is Island Lake. Groundwater drainage lakes are like seepage lakes when it comes to phosphorus sources. The practices around the shoreline are the main impact to the water quality of the lake.

The third type of lake is a drainage lake. Drainage lakes have an inlet(s) and outlet(s). These lakes are the most common around Detroit Lakes, and include the Cormorant chain, Detroit, Sallie, Melissa, and Pelican Lakes. Phosphorus sources to drainage lakes include both land practices upstream in the watershed and practices directly around the shoreline. To understand the inputs and outputs of phosphorus to drainage lakes, it is helpful to measure phosphorus concentrations at the inlets and outlets. Also, since chains of lakes can be managed as a group, they are often formed into watershed districts such as the Pelican River Watershed District and the Cormorant Lakes Watershed District.

No matter what type of lake you spend time on, it is important to think about phosphorus sources to the lake and what practices could be affecting the water quality. If you determine what type of lake your favorite lake is (seepage or drainage), you will know better where to focus your efforts to control phosphorus and protect the lake.

Enjoy the lakes!

(Moriya Rufer is the Lakes Monitoring Program Coordinator for RMB Environmental Laboratories in Detroit Lakes, 218-846-1465,