Is My Lake Safe?

Many factors affect lake and stream health, but the three issues that most often put humans and pets at risk are mercury in fish, E. coli bacteria, and harmful algae blooms.

So how can I stay safe when enjoying lakes or rivers?

  • Sign: Beach closed due to water qualityLook for and obey beach closures.
  • Wait at least a couple days after a rain before swimming.
  • Look for signs of poor water quality, such as algal blooms and dirty or turbid water.
  • Do not swim in water that smells like rotten eggs or sewage.
  • Avoid swimming near pipes that drain into lakes or streams.
  • Before fishing, check the Minnesota Department of Health website for advice on eating fish from specific lakes and streams. Some lakes have too much mercury and you might need to eat fish from those lakes less often.

What are common causes of water pollution?


Mercury is created by power plants burning coal to create electricity, releasing mercury into the atmosphere — which eventually falls across the landscape. Once in the water, fish can ingest it, and people can too, when they eat fish.


Too much bacteria in water can result from leaking septic systems, sanitary sewer overflows, farm animals, pets, and wildlife, and can make people sick and kill pets.

Excess Nutrients

Child swimming in green lakeToo many nutrients, such as phosphorus from decomposing organic material like grass clippings and leaves, can cause algae to grow. Too much algae can be harmful to fish and other animals. Under certain conditions, toxic algae blooms form, such as blue-green algae, which can kill dogs and make people sick.


Sediment can run off the land and cause lake water to be murky and dirty. High amounts of sediment in lakes and streams can ruin fish and other aquatic animals’ habitat.


Chlorides mainly come from salt applied to roads, parking lots, and sidewalks. High chloride levels in lakes and streams can stress and kill fish and other aquatic life.


How can I help to protect my local lakes and streams?

Learn the six steps you can take at home to help improve water quality.


Want to know more?

For information about lake water quality, clarity, and fish consumption advice, visit the MN DNR website.

Contact your local public health department to find out if a lake’s water quality is monitored. Find your Local Health Department or Community Health Board.

Get general information about water quality in Minnesota.

View the Minnesota Impaired Waters map (waterbodies evaluated to below water quality standards).

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