The waters of Buzzards Bay along the Falmouth coast are a muddy brown color because of an algal bloom, but an expert says it should not affect people’s health.
Volunteers for the Buzzards Bay Coalition are reporting drastically reduced water quality this year, said Tony Williams, director of the monitoring program who oversees weekly sampling for water quality all around Buzzards Bay.
“The water clarity is about half of what it’s been in previous years,” Mr. Williams said. “What this means is that the water clarity just seems very cloudy, and there is this green and brown color in the water column.”
Don Anderson, an expert in harmful algal blooms at the Woods Hole Oceanographic Institution, said this particular type of algae is not harmful to humans. “It’s actually something that happens every year at this time,” he said.
The algae, named Cochlodinium, usually bloom in July and August in this area and are sometimes referred to as a red tide or brown tide. “There’s no dangers that I know of to humans from these kinds of big red tides of Cochlodinium,” Dr. Anderson said.
Cochlodinium does not make toxins that are harmful to humans, but can affect shellfish and some kinds of fish, he said.
The algal bloom can also cause damage to the ecosystem when the bloom gets so big that there are no more nutrients to feed on. “The bloom will crash, as we call it, and all of these cells will die and fall to the bottom of the water,” he said.
The algae will decay and use up the oxygen in the water, which can cause fish kills. These particular algae also produce a slimy residue that can coat fish and kill them.
To measure water clarity, volunteers lower a black and white disc at the end of a measuring tape and write down how far they can see the disc.
George R. Hampson of North Falmouth measured the water clarity as low as 30 centimeters in some places, a depth of about a foot.
“People who go swimming cannot see their feet,” Mr. Hampson said.
Some Woods Hole residents compared it to swimming in the Mississippi River. A summer resident of West Falmouth said the water was the color of lemon Jello.
Other volunteers farther north from Pocasset Harbor to Onset Bay are reporting similar measurements, Mr. Williams said.
Cochlodinium can grow very quickly in the right conditions of warm water that is rich in nutrients. Each alga can divide every two days, Dr. Anderson said.
But the visual impact of the algae bloom can be somewhat deceptive, Dr. Anderson said, because these particular algae swim to the surface of the water making them much more visible.
Dr. Anderson said the term “red tide” is not useful, because it means different things to different people. Red tide can refer to algae that turn the water a red color, or algae that are usually not visible which makes shellfish dangerous to eat.
“It doesn’t do anybody any good to characterize them by a color,” he said.