Minnesota is adding another 500 lakes and rivers to the list of waterways with pollution problems.

That list, kept by the Minnesota Pollution Control Agency, now has more than 3,638 lakes and river segments that are considered "impaired" because they are unsafe for drinking or swimming, the fish are unsafe to eat or because the native plants and animals are unhealthy.

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The problems range from too much nitrogen and phosphorus fertilizer to too much dirt and sediment to mercury contamination, PCB's and bacteria that closes beaches for fear the water could make people sick. More than 1,200 waterways have fish with too much mercury to be considered safe for everyone to eat.

The PCA will hold a public meeting on the newly updated list in Duluth from

1-3 p.m. Thursday at the agency's regional office, 525 Lake Ave. S. in Canal Park.

The state's impaired waters list is updated every two years as new lakes and rivers are tested. About 40 percent of all the lakes and segments of rivers that are tested end up on the impaired list, which kick-starts state action to fix the problems, such as enacting a public process and cleanup plan, including so-called Total Maximum Daily Load plans. About 900 plans to clean up waterways have begun, but only 15 waterways have graduated off the list.

The PCA is proposing taking four more waterways off the list this year because those waters got cleaner.

The state has now tested 21 percent of the state's 81 major watersheds. The state hopes to get to every waterway once every 10 years. Minnesota has about 12,000 lakes and 70,000 miles of rivers and streams.

The list is developed by the PCA and then sent to the U.S. Environmental Protection Agency for approval after an extensive public comment process, all under the federal Clean Water Act.

The Freshwater Society has a website -- checkmylake.org -- that allows people to see if their favorite waterway is impaired and why. For more information on the state's impaired waters effort, go to pca.state.mn.us.