Is it safe to fish and swim?

How can you determine if your favorite local lake is safe for fishing and swimming? In Minnesota, the Pollution Control Agency (MPCA) works with local government and volunteers to monitor water quality in lakes, rivers, and streams, and maintains a list of water bodies that are “impaired” by one or more pollutants. Common impairments include high levels of mercury in fish (a concern if you are fishing), as well as nutrients that cause algal blooms, bacteria that make people sick, and sediment that clouds the water (all of which are concerns if you are swimming).

Though water quality data is collected and updated regularly, finding the information online isn’t terribly intuitive. My recommendation is to use a two-step approach that references the MPCA’s Impaired Waters Viewer (most easily found through an internet search) and the Minnesota Department of Natural Resources’ (DNR) Lake Finder (www.dnr.state.mn.us/lakefind).  

MPCA’s impaired waters viewer is an interactive online map that shows impaired waters in red, delisted waters in purple (lakes and streams that are no longer impaired), and all other water bodies in a subtle background blue. Brace yourself before opening the map for the first time, because the onslaught of red is fairly alarming.  

If you click on a red lake or stream on the map, a pop-up box will appear with information about the impairment. Note however, that you might need to reference the glossary of terms (i in the upper right corner) to decode the information. For example, if you click on White Bear Lake, you’ll see a pop-up box that says “Impaired use: AQC” followed by “TMDL approved for: Hg-F.” This means that White Bear Lake is impaired for aquatic consumption (AQC) due to too much mercury (Hg-F) in some of the fish that live in the lake.

Next, head to the Minnesota DNR’s lake finder to learn more about the lake that you are researching, including its size, depth, and types of fish species found in the lake. If there is a fish consumption advisory due to mercury or another pollutant, you can click the blue box at the top of the page to learn more about that as well. In the example of White Bear Lake, anglers are encouraged to follow Minnesota’s Statewide safe-eating guidelines. Sometimes, however, there will be specific guidelines for a lake, such as “don’t eat crappies more than once per week.”

Mercury contamination from atmospheric deposition is the most common cause for water quality impairment in Minnesota and it affects 1608 lakes and rivers in Minnesota, including many otherwise pristine lakes. In fact, a quick perusal of the impaired waters viewer shows numerous lakes in northern Minnesota with mercury impairments, including many in the Boundary Waters Canoe Area Wilderness.

Now, let’s consider another common scenario you might find in the impaired waters viewer. If you click on Colby Lake in Woodbury, the pop-up box will say “Impaired use: AQR” followed by “Additional impairments: Nutrients.” This means that Colby Lake is impaired for aquatic recreation (AQR) due to high levels of nutrients that fuel excess algae growth and periodic algal blooms. There are 744 water bodies in Minnesota impaired by excess nutrients and the problem is most common in agricultural and developed areas.

If your lake has a nutrient impairment, you’ll want to pay close attention to what the water looks like during the year and will need to avoid swimming or wading if the water turns green like pea soup, has green swirls that look like spilled paint, smells bad, or you see poop-like blobs floating in the water. All are indications of a possible blue-green algae bloom, which can be toxic to people and pets. Note, however, that duckweed (looks like miniature lily pads floating on the water) and filamentous algae (looks like stringy green sea monster goo) are both normal aquatic plants that grow in lakes and aren’t a cause for concern.

If you learn that your favorite lake is impaired, there are many ways you can get involved to help turn it around. One of the most important actions you can take is to join the lake association (if there is one) and attend meetings and events held by the lake association and/or watershed district to share your concerns. Another simple thing you can do is to adopt your nearest storm drain (mn.adopt-a-drain.org) to help keep litter and debris from roadways out of the water. Lastly, if you own a home, you can change your landscaping practices to minimize the use of fertilizers and chemicals and incorporate more native plants. See BlueThumb.org, mnwcd.org/planting-for-clean-water, or dnr.state.mn.us/rys for more info on how to get started.