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Waters in state cleaner

By John Weiss

weiss@postbulletin.com

The list of Minnesota streams, lakes and rivers contaminated with too much bacteria from waste, sediment or phosphorus shot up 24 percent in two years.

But overall, the state’s waters are considerably cleaner.

That’s not a contradiction.

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On the one hand, the number of impaired waters in a list given to the federal government grew from 1,182 in 2006 to 1,469 for the list the agency proposes to submit next year. The Minnesota Pollution Control Agency recently came out with its draft list of waters with pollution levels that rose above a threshold limit.

What that reflects mostly is that more water has been tested in part because of a new push statewide to determine levels of contamination, then to find ways to lower those levels. The percentage of lakes or stretches of streams and rivers put on the list after being sampled, however, remains at about 40 percent, said Dan Helwig, MPCA director of biological monitoring.

That will vary considerably by stretch of water or region of the state.

For example, headwaters of a trout stream probably wouldn’t be so turbid or have so much bacteria that they meet the standards; at the stream’s mouth, however, the stream might have picked up enough pollutants to exceed standards.

Mercury, which is found across the state, is also variable. In the same lake, larger fish of a species would exceed levels, while smaller ones wouldn’t.

Regionally, the chances of having a stream with excessive turbidity or bacteria are better in the southeast than the northeast because the southeast has more farming and cities, said Bill Thompson, an MPCA research scientist in Rochester.

Within each affected stretch, results will vary depending on weather. Turbidity and bacteria will crash in a drought, but spike dramatically with 3 inches of rain.

When the state looks at all the sources of contamination throughout the state as part of the Minnesota Milestone River Monitoring Program, it’s finding that things are getting better, while ammonia continues to rise, Helwig said.

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Phosphorus, ammonia, biological oxygen demand, total suspended solids and fecal coliform showed general decreases, or at least stayed the same in most cases.

That’s because of efforts over the past few decades to make better use of farm chemicals or better control of soil washing off urban sites into water. The MPCA has been checking nearly 100 sites, including 12 in this region, to find those trends.

While the milestone doesn’t show mercury, it, too, is dropping because mercury has been cut out from many common household items or is being better controlled from other sources such as coal-fired power plants.

For more information on impaired waterways, visit www.postbulletin.com/weblinks.

MPCA’s report on impaired waterways

http://www.pca.state.mn.us/water/tmdl/tmdl-303dlist.html

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