In this June 11, 2015 photo, A field of cereal rye grows on land farmed by Wayne Siela in Vinton, Iowa. Siela says part of the rye is used to grow cover crops near creeks and streams to help filter water runoff from their crop land. Nitrogen pollution flowing out of Iowa to the Gulf of Mexico has grown by close to 50 percent over nearly two decades, a new report shows, despite hundreds of millions of dollars spent to stem nutrients entering the state's waterways. Environmentalists say the study raises new questions about the effectiveness of Iowa's approach to improving water quality and its reliance on voluntary ag compliance.(Michael Zamora/The Des Moines Register via AP)
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