A fish kill occurred in Cowpen Creek. (Video courtesy of Scott Sewell)

More than 100,000 fish have gone belly-up in the Middle River area of eastern Baltimore County in what state environmental officials are calling the biggest fish kill of the year.

The Maryland Department of the Environment said Friday it's still investigating the cause of the die-off, which began this week. But preliminary findings suggest the fish were poisoned by a toxin produced by algae, spokesman Jay Apperson said.


The toxin does not harm people or other animals, he said.

Among the species killed were largemouth bass, yellow perch, bluegill, crappie, sunfish, carp and Atlantic menhaden, Apperson said. They were found in the upper Middle River and in several tributaries, including Norman, Hopkins and Dark Head creeks.

Scott Sewell of Middle River said he heard about the kill Wednesday and contacted state officials after seeing hundreds of dead fish in the water around Wilson Point Park. On Thursday, he said, he took two state investigators out on his boat, and they saw thousands of dead fish in neighboring waterways. Dead fish were particularly thick in Martin Lagoon and Cowpen Creek, he said.

"It was just so heartbreaking," said Sewell, 65, who is a part-time fishing guide and conservation director of Maryland Bass Nation, a sportfishing group.

Apperson said the department received reports of dead fish as early as Monday and visited the area three times during the week to collect water samples and fish tissue. Analysis of the water found a type of harmful algae, Karlodinium veneficum, in high enough numbers to produce a toxin capable of harming fish.

Karlodinium blooms typically occur in late spring or summer. Apperson suggested warm weather this fall may have allowed the algae to survive and grow, while recent drops in water temperature could have triggered its demise.

There have been about 80 smaller fish kills statewide this year from a variety of causes, including pollution and lack of oxygen in the water for fish to breathe. Apperson said investigators have seen no evidence of toxic chemical pollution in this case, but have sent water samples to the University of Maryland for further analysis.

Apperson noted that excessive levels of the nutrients nitrogen and phosphorus can lead to algae blooms. Middle River and all of the Chesapeake Bay are afflicted with an overdose of those nutrients from wastewater treatment plants and from rainfall washing fertilizer, animal waste and other organic material off farmland, lawns, streets and parking lots.

"It is another example where these events are happening with greater frequency and with greater impacts around the globe," said Patricia Glibert, a professor with the University of Maryland's Center for Environmental Science who has studied harmful algal blooms.

She and other Maryland researchers reported earlier this year that there had been a sixfold increase in Karlodinium blooms in the bay, from fewer than five per year in 2003 to more than 30 in 2008. They often appear late in summer when waters are warmest and have been linked to fish kills as well as to problems with the development of oysters.

The Chesapeake Bay Foundation noted that this week's fish kill came just a few days before the Baltimore County Council is expected to vote to repeal stormwater fees levied on all property owners. The fees — which range from $14 a year for a townhouse to $26 a year for a single-family home — pay for stream restoration and other measures meant to curb polluted runoff.

"Clearly the streams and rivers in Baltimore County are not healthy for fish — and for people," said Tom Zolper, spokesman for the Annapolis-based environmental group. "The money that was being collected from stormwater fees was meant to address this issue."

The council is set to vote on repeal Monday. All seven council members support repeal, though County Executive Kevin Kamenetz has opposed it. Council members say the fee is a burden on homeowners and businesses, and that the county has enough money to pay for needed projects without the fees.

The foundation has warned that the county could run afoul of state law unless officials spell out how they will pay for pollution control projects required as part of the bay restoration effort.


"We can expect more of these fish kills if this problem of polluted runoff isn't addressed," Zolper added.