Why are 1,000 dead fish floating on surface of Baltimore's Inner Harbor?

A reported fish kill has left approximately 1,000 dead fish and other species on the surface of Baltimore's Inner Harbor, according to the Maryland Department of the Environment (MDE).

The MDE says fish kill spreads along the Canton Waterfront Park to South Ann Street and near the Domino Sugar plant.

Officials documented approximately 1,000 dead menhaden, 126 dead blue crabs, and a small number of other fish species at the surface. 

What caused the fish kill?

The MDE says the fish kill is likely caused by low dissolved oxygen linked to a localized "Pistachio Tide" event.

A sulfur bacteria bloom creates a green surface sheen and produces a sulfur odor as it decomposes, depleting oxygen in the water, the MDE said.

Menhaden are essential to Maryland's wildlife, serving as a food source for birds and other sea life.   

Previous fish kill in the harbor

In 2025, there were at least three fish kills in Baltimore's harbor within weeks.

Last September, the MDE estimated that 25,000 dead menhaden were found in the water from Canton to Locust Point. 

On August 28, 2025, MDE said it found at least 120,000 floating dead fish between Harbor Point and Fort McHenry.  Days earlier, a weather-related fish kill saw 61,000 dead fish in the harbor.