Billions of microorganisms are creating a bright green sheen - and a potential hazard - at Hopkins Pond in Haddonfield.
"Cyanobacteria are in the water," explains Mike Haberland, environmental and resource management agent with the Rutgers Cooperative Extension in Camden County.
His dramatic photographs of the bacteria in full bloom, taken Thursday, led the county parks department to install warning signs about the "potentially harmful" organism.
The bacteria release a toxin into the water when dying or damaged. But their proliferation seems to be something more than a nuisance, yet less than a crisis.
"We don't have to cordon off or close the area," department director Frank Moran says.
"The main thing is for people to keep their pets out of the pond."
Haberland shares weekly water samples he collects from Hopkins with the New Jersey Department of Environmental Protection, which "is developing strategies for dealing with cyanobacteria," spokesman Larry Hajna says.
"Hopkins is a pilot [site] that's very important to us," he adds. "We're reaching out to county health departments to help them understand and better identify cyanobacteria. People need to know how to identify it as well."
Eager to see for myself, I meet Haberland at the edge of the lovely little pond.
He advises me to avoid falling in - because he doesn't want to have to jump in to pull me out.
"I don't touch this water without gloves," he says, pointing to wispy whorls of green that cover much of the sunny surface.
"That's them," Haberland adds. "These unicellular critters like to bunch up together."
The dominant strain of cyanobacteria found at Hopkins is called microcystis. Ingested in sufficient quantities, it can cause canine liver damage. It also can irritate human skin.
Other strains are fouling Smithville Lake in Eastampton, Burlington County, and Mercer Lake in West Windsor, Mercer County.
Sometimes referred to as "blue-green algae," cyanobacteria like hot, dry, late-summer weather and shallow, stagnant or slow-moving water that's high in phosphorous and other nutrients.
"This year is a particularly heavy bloom," says Haberland.
He first found the microorganisms in Hopkins Pond six years ago, after a fish kill was reported there. Two years later, the county installed six aerators, or "bubblers," along the bottom of the pond.
The devices oxygenate the water and seemed to be helping control the blooms - until this summer. "I'm concerned," Haberland says.
He praised the state and the county, including the Camden County Soil Conservation District, for helping provide resources to monitor and perhaps eventually solve the pond's cyanobacterial problem.
"We need to get a handle on where the trigger is that is causing these blooms," Haberland says. "There's a lot of organic life in Hopkins Pond. There's a lot of stuff in there."
Hopkins Pond was created in 1789 by damming the Hopkins Mill Branch, a tributary of the Cooper River. It covers about 4.3 acres and is as much as 12 feet deep in places.
Surrounded by lush woods and a popular walking trail, the water is used infrequently by canoeists and kayakers, although some folks do fish there. Moran notes that the county strongly advises people not to eat fish caught in any of its waterways.
"We've been working with Rutgers on small solutions for Hopkins for years," he says. "We're committed to hiring a water quality specialist to do some additional, more detailed testing and see what our options are."
Although cyanobacteria can be killed by common algicides such as copper sulfate, "it's a bad idea to kill them when they are in a bloom stage, because they would all release the toxin into the water at once," Haberland says.
Applying the algicide earlier in the year might be better, but also "might be more of a hit-or-miss sort of thing," he adds.
Another possibility? Ultrasonic treatment.
"You can use a transducer to break apart the part of the cell that enables [the bacteria] to float, so they fall to the bottom and decay slowly," Haberland says.
"The technology isn't cheap. But it is available."
For an ancient, primitive life-form that's neither plant nor animal, cyanobacteria do seem rather . . . sophisticated.
They can't swim, per se. But they can change their position in the water by utilizing a minuscule sac inside their single-celled body to regulate their buoyancy.
And their visibility changes with the weather, the wind, and the time of day.
During a late afternoon visit to Hopkins Pond on Monday, Haberland calls to give me an update.
"It almost looks clear," he says. "But they're in there."