Approximately 8000 dead fish of 15 species were found on the Chesaeake Bay side of the Patuxent River Naval Air Station on July 2nd; the investigation suggested the kill occurred one day earlier. Maryland Department of the Environment reported that witnesses had observed dark colored water and crabs at the water surface or on the beach. Water quality at the location on July 2nd however was normal (8.9 mg O²/L). Moderate densities of the possibly toxic dinoflagellate Karlodinium micrum were reported from a water sample collected at the site.

Nearby Gooses Creek was discovered to have freshly dead and dying Atlantic silversides. Water quality indicated strong algal bloom conditions with dissolved oxygen at 154% of saturation levels and pH of 8.63. A water sample revealed bloom levels of K. micrum at 56,915 cells/ml. Additional water samples and weak but live silversides were collected for further lab analysis.