The Minnesota Pollution Control Agency has spent years documenting and monitoring all 80 of Minnesota's major watersheds in order to gain data about the health of the state's rivers, lakes and streams.

The Minnesota Pollution Control Agency has spent years documenting and monitoring all 80 of Minnesota's major watersheds in order to gain data about the health of the state's rivers, lakes and streams.

Pollution control agency staff members are now revisiting places that were first tested a decade ago, Minnesota Public Radio (http://bit.ly/2vBsQvu ) reported.

Water is sampled from every watershed yearly to check for clarity and pollutants, and intensive monitoring is done on a rotating basis about every eight to 10 years. The sampling includes studying fish found in the watersheds.

"We want to capture every single species, every fish," said Chad Anderson, an agency biologist. "The little species are sometimes just as important as the big ones."

The fish can tell a better story about the water's state than just taking water samples, Anderson said.

"These fish live in the stream, so they're continuously being affected by what's happening around them," he said.

The biologists sort the fish into different buckets and assess the water's ability to support aquatic life.

"You tend to see greater diversity in the higher quality streams," said John Sandberg, a biologist. "When the streams get really degraded, the more sensitive species start to disappear. So in the really heavily degraded streams, you might just see one or two or three species."

The agency then issues a report on the watershed once it's finished compiling data. Local agencies can use that information to focus their efforts on fixing any problems the agency finds.

Steve Woods, the executive director of the water conservation nonprofit Freshwater Society, said water in the northern part of the state is good, but that many bodies of water in the southern part have pollution.