MIDDLE RIVER, Md. (WJZ) — We now know the cause of the largest fish kill of the year in Baltimore County.

The Department of the Environment has confirmed the presence of toxins produced by algae in water samples collected in the Middle River area.

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The investigation also showed higher than normal salinity levels in the supper areas of Middle River and its tributaries, which can affect the physiology of fish.

The department has found no evidence of any chemical pollution as a cause of the fish kill.

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“The Maryland Department of the Environment has aggressively investigated all aspects of this fish kill, following the science every step of the way,” said Maryland Secretary of the Environment Ben Grumbles. “We know anglers and other citizens are concerned about this, and we appreciate their assistance in raising attention to this issue through social media. We’re concerned too. A fish kill sends a strong signal that something is very wrong, and it underscores the importance of clean water to our economy and our quality of life. We will work in collaboration with Baltimore County and its citizens to reduce the nutrient pollution that can help cause algae blooms.”

An estimated 200,000 fish were killed.

Affected areas include Cow Pens Creek, Norman Creek, Frog Mortar Creek, Hopkins Creek and Dark Head Creek.

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Affected fish include largemouth bass, yellow perch, bluegills, crappies, chain pickerel, pumpkinseed sunfish, carp, killifish, Atlantic menhaden, spottail shiner and gizzard shad.