A fish kill hit the Potomac River over the July 4th holiday weekend, impacting multiple fish species, according to social media posts from the Maryland Department of the Environment (MDE).
MDE scientists launched an investigation after receiving reports of dead fish scattered along a stretch of the Potomac River several miles upstream of Little Falls. The event took place on an extremely hot day that also brought powerful thunderstorms.
During early field work, investigators found affected fish near Sycamore Island along the Virginia shoreline. Water assessments revealed the kill was concentrated mainly in one species — golden redhorse suckers. Water temperatures in the impacted area registered in the mid-90s°F, conditions scientists described as highly stressful for fish.
Based on those initial findings, investigators determined the fish kill had likely come to an end or had significantly slowed, and that extreme heat was the most probable cause.
The next day, MDE crews returned to the river for a second round of fieldwork to gather more data and verify their early conclusions. Teams took additional water quality readings, mapped the full extent of the kill, identified the affected species, and collected fish samples for laboratory testing.
On July 6th, MDE announced that the fish kill covered approximately 13.7 river miles, stretching between White’s Ferry and Violette’s Lock (lock 23), located several miles upstream of Sycamore Island.
MDE said the initial investigation turned up no signs of a chemical spill or any other pollution-related event. Further lab analysis and continued field observations are expected to confirm the cause and rule out any other contributing factors.
