In 1996, Illinois added Lake Decatur to its pollution list after farm runoff harmed its water. 28 years later, nitrogen levels fell below the 7.8 mg/L limit

For nearly three decades, Lake Decatur has been at the center of a continuing effort to improve water quality in central Illinois. The lake was added to Illinois' impaired waters list in 1996 because of nitrogen and phosphorus pollution linked to agricultural runoff.

Since then, conservation work across the watershed has focused on slowing runoff, reducing nutrient and sediment loading, and protecting the lake as an important drinking water source.