Small Stream in Northern Indiana (image) US Geological Survey Share Print E-Mail Caption A small stream flows through corn fields in northern Indiana. A new USGS report shows that drought periods followed by rainfall caused nitrate levels to increase to the highest ever measured in some Midwest streams during a 2013 study. Credit Credit: USGS Usage Restrictions Credit: USGS Share Print E-Mail Disclaimer: AAAS and EurekAlert! are not responsible for the accuracy of news releases posted to EurekAlert! by contributing institutions or for the use of any information through the EurekAlert system.