Seasonal temperature changes combined with polluted water, algal blooms, and dead zones, created deadly conditions for fish in the Baltimore Harbor on Wednesday, September 4. State officials identified roughly 24,000 dead fish in the Harbor, mostly menhaden. Menhaden are a key species in Chesapeake Bay food chains, but concerns are mounting over their numbers in the Bay.
Baltimore Harbor educators with the Chesapeake Bay Foundation (CBF) observed the dense algal bloom on Tuesday, noticing the water’s stark change in color and sulfur-like smell. On Wednesday, mounds of floating dead fish followed.
While small fish kills are a natural occurrence during seasonal changes—when days are warm and nights are cold—this magnitude is alarming. To compare, in late August a similar algal bloom killed approximately 1,700 fish.
Thermal inversion in the water column, which contributed to this fish kill, occurs when cooler, denser water sinks to the Harbor bottom, and lifts up warmer water and sulfur bacteria. These bacteria photosynthesize like plants, but consume oxygen rather than producing it, and release the “rotten-egg” smell currently permeating the Harbor.
At the same time, algae have been thriving on a diet of nutrient-rich stormwater runoff and pollution, and enjoying waters warmed by climate change. A recent report by the Environmental Protection Agency (EPA) showed that, despite improvements in many clean water metrics, Maryland is failing to make progress on stormwater remediation, holding back progress on overall Bay health and contributing to the possibility of additional fish kill events.
Though thermal inversions, sulfur bacteria, and algae occur naturally, their impact on Harbor life is greatly exacerbated by pollution and climate change. Having to combat stressors from all angles, both natural and man-made, makes fish highly vulnerable. Climate change and pollution only make these conditions worse.
Gussie Maguire, CBF Maryland Staff Scientist, issued the following statement:
“It's crucial that we limit further stressors on our beloved aquatic species. Menhaden are the bedrock of the Bay ecosystem, supporting many other species’ diets. They already face immense pressure from industrial fishing lower in the Chesapeake Bay. Reducing nutrient pollution from stormwater runoff in Maryland would help expand habitat for these critically important fish. Right now, the Bay’s menhaden are pinched between industrial fishing and dead zones.
“Earlier this year, an EPA progress report showed that Maryland has made zero progress on reducing polluted stormwater runoff from entering our waterways. Pollution from stormwater has outpaced any management improvements due to increased development pressure and more intense rainfall from climate change. If our regulations remain par for the course, wildlife and people will continue to suffer.”
