John Neukam has been catching crabs in pots near the Middle River for decades. But this year, the crabs have been dying in the water, suffocated by a bright green algae bloom that is choking off oxygen and worrying watermen and recreational boaters.
"You crab all week, you get a bushel and a half in your live box, and they die," said Neukam, after checking his pots yesterday morning. "I've been here all my life - 64 years - and we've only had this one other time, when fertilizer from a farm seeped into the cove."
People who live in subdivisions off the coves and creeks in the Middle River area have been scared to eat the fish they catch, worried about letting their children and dogs swim in the water, and in some cases unable to get their boats out from their docks, which have been socked in by the thick, carpet-like algae.
The state Department of Natural Resources says the algae is not toxic, but it is alarming. When the algae dies, the decomposition sucks the oxygen out of the water, killing crabs and fish. The algae also blocks sunlight from the beneficial bay grasses, which provide a refuge for shellfish and crabs.
The area that has seen the algae explosion is home to striped bass, white and yellow perch, catfish, Atlantic needlefish, chain pickerel and other species.
"This is an important area for commercial harvest of eels and catfish," said Mike Naylor, a DNR biologist who was checking out the bloom in the Baltimore County waterways yesterday. "We don't want a fish kill."
But there is little the state can do to fight the stringy, filamentous algae, which clumps together like knots of tangled green hair.
In smaller amounts, algae is a natural part of the ecosystem, but it is cropping up in huge patches throughout the Chesapeake Bay, a reminder of the impact people and development can have on the estuary and the fragile nature of the small coves and fingers that branch off of it. Such blooms are commonly caused by excess nutrients, including nitrogen and phosphorus, which come from such things as fertilizer and auto exhaust. The pollutants run off the land into the water.
"We have a lot of people in these watersheds and very little forest cover left," Naylor said. "So our waters have more nutrients than they should, and they're warmer than they should be, so these things combine to allow algae to thrive."
The type of algae causing havoc off the Middle River is multicellular, different from the floating single-celled algae that is more common throughout the bay.
This recent bloom comes in an area that has seen a resurgence in bay grasses, helped along by aggressive DNR plantings. The grasses help to filter nutrients from the water and produce oxygen. DNR has documented significantly higher populations of crabs in areas with grasses than in those without.
"We were so excited about the grasses, and then this happened and we were like, 'Oh, no!' " said Jim Mitchell, who lives on Browns Cove and is environmental chairman of the Holly Neck Conservation Association. The algae grows on the grasses, but officials say there's no reason to think the grasses cause the algae.
Mitchell, 54, a polygraph examiner for the state police, has lived on the cove since 1973 and said he has never seen a bloom as severe as this one. Coming into the neighborhood at night, he said, you can smell mildew from the dying algae.
"The community is really upset about it," he said.
Naylor said he has received more than 50 phone calls about this bloom - more than he has received for any environmental event in 15 years at DNR.
In this area of Baltimore County, where expensive houses are clustered along the water but still close enough to the city for residents to commute there for work, people expect a certain level of quality from the bay. And when the algae gets so thick that it clogs the intakes of their boats, they register their complaints.
"If we had this on the Eastern Shore, we might get one phone call," Naylor said. "But we have it in Baltimore County, and the phone is off the hook."
The Maryland Department of Environment is trying to determine the cause of the bloom, a spokesman said. Officials said the bloom is likely to get smaller but to be around for the rest of the summer.
There is one theory that the bloom could be a sign of progress. A study in New England found that multicelled algae was highest when nutrients were at a moderate level, said Peter J. Tango, the Chesapeake watershed monitoring coordinator for the U.S. Geological Survey. High levels of nutrients led to less multicelled algae, the study found.
"Tantalizing thought: Is this bloom evidence of a direction of positive change we want to see in the bay?" Tango said in an e-mail interview. "I can't say for sure. ... We can take note for now and consider it something to watch in the years ahead."
Out on the water yesterday, the algae was hard to miss. Boaters who spotted Naylor and two other DNR biologists in their aluminum vessel would pull alongside to ask about the algae. The scientists had few answers, except to say that it wasn't dangerous but certainly a nuisance.
"It looks like a soccer field over there," Naylor said, surveying an especially large cluster of the green stuff yesterday. He took out a camera to take pictures. The algae's life cycle is just a few days, he said, so you can have a huge bloom followed by a huge die-off, creating big swings in the oxygen level in the water.
As the boat motored along, he saw a dead carp floating on top of the algae. He couldn't say what had killed it, but he didn't want to see any more.
Sun reporter Rona Kobell contributed to this article.