Why are 5,000 dead fish floating on surface of Baltimore’s Inner Harbor?
By Adam Thompson, Tara Lynch
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BALTIMORE (WJZ) — A reported fish kill has left approximately 5,000 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 5,000 dead menhaden, 126 dead blue crabs, and a small number of other fish species at the surface.
The dead fish have caused a stench from Canton to the Inner Harbor.
“Smells kind of like a cross between rotting garbage and an outhouse at a festival,” said Richard Korecky, a visitor from Texas.
What caused the fish kill?
Experts say a one-two punch of the drought and heat wave likely caused the smell and dead fish.
The MDE says the fish kill is likely caused by low dissolved oxygen linked to a localized “Pistachio Tide” event because of the 30-degree temperature difference between this week and last week.
“For it to happen this early is kind of unique, and a lot of it is likely due to the fact that it was so hot here last week,” said Charmaine Dahlenburg, director of conservation at the National Aquarium. “We were in temperatures over 100, and then we dropped down to the 80s.”
Typically, this type of natural event happens in the fall during an annual “turnover” when the days are significantly warmer than the nights. This causes the surface water to cool and sink to the bottom of the harbor, causing bacteria from the floor to rise.
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.
The National Aquarium said it began receiving reports of the smell and dead fish on Wednesday.
These bacteria don’t require a lot of oxygen. At the surface, non-oxygenic photosynthesis takes place, and a sulfur-like byproduct creates not only the smell but the green hue.
The drought likely caused an algae bloom, too. Because the area hasn’t had significant soaking rain, the water stays still and doesn’t mix, causing algae to grow.
Menhaden are essential to Maryland’s wildlife, serving as a food source for birds and other sea life. They are also used in fish oil pills as well as pet food.
Blue crabs are also dying because of these phenomena.
“Think about how long you could hold your breath underwater, so it’s very taxing to these animals,” Dahlenburg said.
The smell is likely to last for a few days and a heavy rain storm will make it go away, according to the National Aquarium.
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.
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