Evaluating our Lakes

In Minnesota, our lakes are one of our most precious resources. Even our slogan, “The Land of 10,000 Lakes” boasts of our pride in our lakes. Not much can top the feeling of watching the sun set over the water, swimming on a hot, humid August day, or catching a big walleye. It would be hard to imagine a future without being able to enjoy these activities.

Many of our human activities affect lake water quality. By becoming aware of these activities and changing our behavior, we can decrease our impact on lake water quality. Ottertail County has the most lakes of any county in the entire United States – those are a lot of resources to protect!

Every lake is different due to many factors including surface area, depth, surrounding landuse practices and  climate. Overall lake water quality can be summarized well by three measurements, total phosphorus, chlorophyll-a and water transparency (Secchi depth).

Generally, the more phosphorus there is in the lake the lower the water quality. Phosphorus is food for plants and algae, so the more phosphorus there is in the lake, the more plants and algae can grow. Phosphorus can enter the lake through runoff from agriculture, fertilized lawns, erosion, manure, improperly maintained septic systems, leaf and yard litter, and many other sources.

Chlorophyll-a is the pigment that makes plants and algae green. Chlorophyll-a is measured in lakes to determine algal concentration. A high measurement of chlorophyll-a means that there is a large amount of algae in the lake.

Water transparency is how deep sunlight penetrates through the water. Transparency depends on the amount of particles in the water. These particles can be algae or sediment from erosion, the more particles – the less water transparency. In other words, when the water is murky or cloudy and contains a lot of particles, the light cannot penetrate as deeply into the water column. Water transparency is measured with a Secchi disk. Secchi depth can vary throughout the summer, and it is important to get readings at least every other week, if not every week. After large storms and above average rainfall events, the water clarity can temporarily decline due to all the particles that wash into the lake.

These three water quality measurements are related. Total phosphorus (TP) is a “cause” parameter, while chlorophyll-a and Secchi depth are “effect” parameters. When TP increases, that means there is more food available for algae, so algal concentrations increase. When algal concentrations increase, the water becomes less transparent (cloudier) and the Secchi depth decreases.

Why Monitor Lakes? “Lake water quality assessment information is useful to anyone involved in lake management in Minnesota, from lakeshore owners to lake associations. It provides lake water quality criteria, which can improve how we manage our lake resources and how we measure current conditions. It also provides a knowledge base that we can use to protect and restore our lakes.” – Minnesota Pollution Control Agency (MPCA)

The first reason for monitoring a lake is to get an idea of its general health. Recreational enjoyment, fishing quality and property values are all tied to water quality. After you determine the lake’s current condition, it is important to monitor water quality each year to get an idea of seasonal variability and year to year variability.

When you have consecutive years of data, you can analyze long-term trends to see if your water quality is improving or declining. As abrupt changes in water quality occur, you’re able to investigate the cause and respond to it. This data can also be useful in lobbying the city or county to support or dispute land use changes around your lake. There are two examples of lakes in Ottertail County that have challenged zoning issues using water quality data – Dead Lake and Pelican Lake.

How do I monitor? There are easy and inexpensive ways to monitor lake water quality. Lake Associations can improve membership and stewardship by involving members in a monitoring program. By using volunteer monitors the amount of data on Minnesota lakes has increased dramatically, since the state has neither the staff or resources to collect water quality on every lake in Minnesota.

When starting a monitoring program on your lake, it is important to first lay out your goals for monitoring. There are four general purposes for monitoring as outlined in the Volunteer Surface Water Monitoring Guide (MPCA, 2003). They are: education and awareness, condition, problem investigation, and effectiveness. The first two purposes (for education and awareness and for determining lake conditions) cover the vast majority of lake monitoring conducted in Minnesota.

The MPCA has a Citizens Lake Monitoring Program (CLMP, http://www.pca.state.mn.us/water/clmp.html) that you can join for free and receive a free a Secchi disk. This program involves just the collection of water transparency data using a Secchi disk.

To get a more comprehensive understanding of water quality and the condition of the lake, it is important to measure phosphorus and chlorophyll-a in addition to Secchi depth. This type of monitoring, (for education and awareness and for determining lake conditions) is the cornerstone of the RMB Environmental Laboratories Lakes Monitoring Program. The Ottertail Coalition of Lake Associations (COLA) has participated in this program for the past 11 years, and the number of lakes involved keeps increasing. In all, over 400 lakes statewide find this program an economical and user-friendly means to characterize nutrient levels and productivity within their lake. For more information, please visit our website, or contact me at 218-846-1465, lakes.rmbel@eot.com.