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Maryland Department of the Environment

Department of the Environment investigates fish kill


Jay Apperson

(410) 537-3003

Department of the Environment investigates fish kill

Largest fish kill of the year appears to be caused by toxin released by algae, no indication that toxin is harmful to people or animals other than fish

Baltimore, MD (November 13, 2015) – The Maryland Department of the Environment is investigating a fish kill in the upper Middle River and several of the river’s tributaries in Baltimore County.

The Department estimates more than 100,000 fish have died in the waterways the past several days. The preliminary results of the Department’s investigation show the cause of the fish kill to be a strain of algae that produces a toxin that is lethal to fish. There is no indication that the toxin is harmful to people or to other animals.

The waterways affected are Norman Creek, Hopkins Creek, Dark Head Cove and the upper Middle River. The fish affected include largemouth bass, yellow perch, bluegills, crappies, chain pickerel, pumpkinseed sunfish, carp, killifish and Atlantic menhaden. The Department of the Environment is providing information on the fish kill to the Maryland Department of Natural Resources and the Baltimore County health department.

The toxin kills fish by inhibiting oxygen uptake through their gills. There is no indication that the toxin bioaccumulates, meaning that surviving fish should be safe to eat. The Department of the Environment issues fish consumption advisories for Maryland waterways.

The Department of the Environment received several reports of the fish kill beginning Monday morning. The Department went to the site to investigate Monday, Tuesday and Thursday. The Department obtained water samples and fish tissue samples. An analysis of the water samples showed the presence of the dinoflagellate Karlodium venificum, with cell counts high enough to produce the toxin. The release of the toxin appears to have been exacerbated by large amounts of the algae dying off simultaneously. Subsequent analysis shows that the cell count levels of the algae appear to be diminishing.

Blooms of this type of algae are typically seen in the late spring or summer months. The warm weather this fall might have allowed the algae to survive and grow, and recent drops in the water temperature might have caused the algae to die.

Excessive levels of nutrients such as nitrogen and phosphorus in the water can lead to algae blooms. Reducing nitrogen and phosphorus pollution from all sources is at the heart of Maryland’s blueprint for Chesapeake Bay restoration.

This week’s fish kill appears to be the largest in Maryland this year. There have been about 80 smaller fish kills this year in Maryland, caused by factors such as low dissolved oxygen levels in water, localized pollution and the discarding of dead fish.

The investigation into this week’s fish kill has not shown evidence of any chemical pollution as a cause. The investigation is continuing. Water samples have been sent to the University of Maryland for further analysis, including confirmation of the presence of the toxin.

Anyone with information on this or any other fish kill or with other concerns on environmental matters involving the Chesapeake Bay or its tributaries should call the Bay environmental hotline at 877-224-7229.


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