Iowa’s 132 lakes are among the water bodies most polluted with fertilizers in the world, according to a study by Iowa State University. Researcher John Downing took three rounds of samples from each of the lakes last summer, and the results turned up heavy concentrations of nitrates and phosphorus, both common ingredients in farm and yard runoff. The nutrients feed algae, which in turn choke off food and oxygen supplies for other plant life and fish. The university has embarked on a five-year study of the lakes.