25,000 Dead Fish Found In Baltimore Harbor

For fish in Baltimore’s Inner Harbor, another mass die-off has struck.

Tourists looked on Tuesday as thousands of dead Atlantic menhaden floated across the water’s surface, filling the harbor with a sour stench. The scene underscored ongoing environmental struggles in both the harbor and the larger Chesapeake Bay.

State officials estimate about 25,000 fish perished in the latest event. Inspectors from the Maryland Department of the Environment (MDE) surveyed the harbor Monday, finding dead fish stretching from Canton through the Inner Harbor to Locust Point.

Unlike a single spill or discharge, regulators say the deaths stem from a combination of factors tied to long-standing nutrient pollution from runoff and wastewater overflows. As algae and organic matter decompose, they strip oxygen from the water — creating conditions lethal to marine life.

This is the third such incident in recent weeks. In late August, unseasonably cool temperatures triggered two far larger fish kills, with one wiping out more than 61,000 menhaden and 400 crabs, and another claiming roughly 121,000 fish. Both rank among the largest die-offs recorded since MDE began tracking them in 1984.

Scientists and advocates say a seasonal algae die-off may have played a role this week, but they also point to another recurring phenomenon: sudden evening temperature drops that churn the harbor’s waters. That turnover brings oxygen-depleted, bacteria-rich water to the surface. When exposed to sunlight, sulfur bacteria thrive, further draining oxygen and leaving the harbor tinted green — a phenomenon known as “pistachio tides.”

“The harbor seems to be trapped in this cycle,” said Alice Volpitta, Baltimore Harbor Waterkeeper with Blue Water Baltimore. “Between algal blooms and these cool weather turnovers, it’s been an especially deadly season for fish.”

Menhaden, often called “the most important fish in the sea” for their role at the base of the bay’s food chain, swim in massive schools and are vital to larger predators. While their overall population has improved in recent years, the recurring kills highlight the fragile balance in the Chesapeake.

Past events underscore the scale of the problem: at least 8,000 fish died over the July 4th weekend this year, about 24,000 were lost in September 2024, and some 25,000 in 2012. The largest recorded harbor kill dates back to 1984, when one million menhaden perished.

25,000 Dead Fish Found In Baltimore Harbor  was originally published on wolbbaltimore.com