Rainfall following drought linked to historic nitrate levels in Midwest streams in 2013

Highest concentrations found in Iowa, Minnesota and Illinois. Drought periods followed by rainfall caused nitrate levels to increase to the highest ever measured in some Midwest streams during a 2013 study. The USGS and the Environmental Protection Agency collaborated in 2013 to sample 100 small streams across parts of 11 states in the Midwest. Scientists tested for a broad range of water-quality and habitat characteristics and assessed organisms living in the stream, including algae, invertebrates and fish. The study did not look at treated drinking water. The nitrate analysis included comparing 2013 findings to 20 years of nitrate results from multiple state and federal agencies for more than 1,000 streams across the region.