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Levels of nitrates and phosphorous are rising in many sloughs of the Wisconsin River, causing concern among anglers from Iowa, Sauk and Columbia counties and the author of a new study suggests the river should be placed on a national list of endangered bodies of water.

Last summer, Dave Marshall, an aquatic biologist, hydrologist and former Department of Natural Resources biologist, conducted a study of the nitrate and phosphorous levels in some sloughs and ponds fed by the Wisconsin River.

Marshall now owns a research consulting firm, Underwater Habitat Investigations and often is hired to conduct such studies.

The results of his Lake Planning Grant Diagnostic and Feasibility Study, sponsored by the River Alliance, were released last week.

Over the last five years, Marshall said he has heard from area anglers and residents complaining of poor water quality and nuisance algae in Lower Wisconsin Riverway sloughs.

Based on Marshall’s findings, there are many more areas of groundwater contamination spanning the entire riverway.

Contaminated groundwater is the primary source of pollution as commercial fertilizer, liquid manure and other wastewater products leach into groundwater, the primary source of water for floodplain lakes and numerous private wells.

“The entire river valley had already been identified as highly susceptible to groundwater pollution,” Marshall said. “But the river sloughs that are spring fed are getting too much nitrogen and phosphorous. Studies have shown fish and aquatic organisms are more sensitive to nitrates than are humans.”

He said the fish can handle two parts of nitrogen per million gallons, and levels are as high as 20 parts per million in many areas.

He studied 13 sloughs between Spring Green and Sauk City and found groundwater contamination of the whole riverway.

He said much of that can be attributed to runoff from farmland into streams.

“There is an influence of groundwater contamination in all these sloughs,” Marshall said. “Sand doesn’t hold nutrients well. To grow crops on poor soil like that, it needs nutrients, or the contamination tends to move into the groundwater.”

Timm Zumm, president of the conservation group Friends of the Lower Wisconsin Riverway, said educating farmers and the public about the issue is an important first step.

“It no longer seems to me that the agriculture producers are questioning that agriculture is the biggest contributor to the nitrates and phosphorous,” Zumm said. “That’s progress. We aren’t pointing fingers, we’re questioning what can we all do to work together to reduce this problem. Everyone seems to agree that putting in conservation buffers will work. If we could get some kind of subsidy like a crop reduction program for conservation easements, then we could move forward.”

Marshall said during the growing season of 2013, there were severe impairments to recreation and water quality from cladophora, a type of algae, and duckweed that rendered the sloughs unusable for recreational angling and boating.

“The degraded conditions found in most of the floodplain lakes are posing threats to the state endangered starhead topminnow and other environmentally sensitive species, particularly the darters that live in cutoff channel oxbow lakes,” Marshall said. “These problems are linked to excessive nutrient applications over coarse sandy soils that rapidly leach nitrates and likely phosphorus.”

He said the best way to mitigate the problems would be to install a buffer system along the river’s shores.

“A buffer width of 200 yards around the slough and planted in the pasture or trees could intercept those nitrates and phosphorous,” Marshall said. “The U.S. Environmental Protection Agency has published literature reviews that state if buffers are established with deep rooted prairie plants or trees, that intercepts a lot of pollution.”

He said areas where there are residences with private wells and forests already intercept a lot of the nitrates.

“That’s an example of a buffer,” Marshall said.

His study also concludes that the State of Wisconsin should adopt U.S. EPA recommended nitrogen criteria.

“The Lower Wisconsin State Riverway floodplain lakes with excessive phosphorus and nitrogen should be placed on the U.S. EPA list of impaired waters,” Marshall said.

Contact Kim Lamoreaux at, or call 608-393-5777

News reporter, Capital Newspapers