Scads of silvery, lifeless fish were seen floating along in the waters of the Baltimore harbor and Back River this weekend.
On Monday, state investigators estimated the kill at around 30,000, mainly Atlantic menhaden, said Jay Apperson, a spokesman for the Maryland Department of the Environment.
Authorities have yet to pinpoint a cause, but suggested that disease may be the culprit. However, Apperson stressed that the investigation is ongoing. He added that lesions were not found on the fish.
Angela Haren of Blue Water Baltimore said she first received reports of a fish kill in the Patapsco River between Key Bridge and Fort McHenry on Friday afternoon. By Saturday morning it had spread to Canton.
Owen Sahnow, 16, noticed what looked to him like thousands of fish around the coastline of Fort McHenry as he rode his bike there over the weekend. "It definitely smelled," he said.
Some have been epic in their proportions. In 1997, an outbreak of Pfisteria caused lesions in fish as well as health problems in watermen. It also spurred a bipartisan effort to clean up the Chesapeake Bay.
Though pollution or disease can kill fish directly, most die-offs are blamed on a lack of oxygen in the water, essentially suffocating them. The shortage is often brought on by an algae bloom that uses up all the life-sustaining air in the depths as the algae — tiny aquatic plants — die off and decompose.
Apperson said investigators took samples of the water and found no indication that pollution was the cause. Fish were found in both the mouth of the harbor and the Back River, suggesting that the problem was not specific to the water of the harbor, Apperson said.
Investigators collected fish that appeared to be dying and examined their tissue. It was possible, Apperson said, that the fish were distressed — and as a result, diseased.