MADISON, Wis. (AP) — A new study details the sources of unnatural green growths of vegetation and bacteria that stink up long stretches of the upper Wisconsin River.

The Wisconsin Department of Natural Resources studied phosphorus pollution in more than 9,000 square miles of the river basin from Lake Wisconsin to Vilas County, The Wisconsin State Journal reported. The study includes Lake Wausau, Big Eau Pleine Reservoir, Lake Du Bay and Lake Delton.

“This effort has spanned almost eight years and builds on previous watershed work conducted in the basin,” said Kevin Kirsch, a DNR water resources engineer who is managing the project.

The pollution is largely caused by farm nutrients carried by rain and snowmelt. The study recommends where to reduce pollution sources in order to return waters to a healthy state.

The department plans to hold a series of public meetings next month to discuss its findings.

“There is still much work to be done to achieve water-quality standards and reduce algae blooms and the other negative impacts associated with excess phosphorus loadings,” said Sharon Gayan, director of the DNR water quality bureau.

The Madison Metropolitan Sewerage District has been leading an effort to pool funds from local governments to reduce farm runoff. Grants are available for farmers who want to see how much they’re contributing to pollution and want to find ways to reduce their contribution through changes in planting practices or manure disposal.

More programs, changes in law and additional funds for volunteer measures are needed to better control all sources of pollution, said Adam Sodersten, spokesman for the Madison-based Clean Lakes Alliance.

“Most importantly it will take a transformational and cultural shift in how we approach lake health,” Sodersten said.