The alarmed calls are coming in: "Foam!" But the phenomenon is naturally occurring and nothing to worry about, say the experts.
Lately, joggers and walkers have noticed a thick, snow-like foam building up along the shores of Canandaigua Lake, particularly at Kershaw Park.
It isn't dishwasher detergent, and it's not an early onset of winter precipitation. Experts say the foam is a naturally occurring phenomenon produced by falling leaves and dying zebra mussels.
The foam surfaces every year and in different seasons, but Canandaigua Lake has not had this much since 2001, said Canandaigua Lake Watershed Manager Kevin Olvany.
The foam occurs when decaying organic matter, mostly fallen leaves, produces a "surfactant" — a fatty, soapy substance that is less dense than the surrounding water.
The surfactant floats to the top of the water, where waves and wind agitate it into a foamy state, much as a washing machine or dishwasher creates suds from liquid soap.
Leaves fall into lakes and streams every year, so the foam is always being produced. It can even surface in the winter, when "it can freeze into odd and interesting shapes," said Stephen Lewandowski, consultant to the Canandaigua Lake Watershed Alliance.
This year, as in 2001, the lake has had a higher volume of foam than normal. The cause, said Olvany and Lewandowski, is a large-scale die-off of zebra mussels — an invasive species native to eastern Europe that was first discovered in the United States in 1988 and in Canandaigua Lake in the mid-1990s.
As each generation of mussels reaches the end of its five- to six-year lifespan, many mussels die at the same time, releasing more organic matter into the water. The extra decaying matter causes more foam.
Studies done by Finger Lakes Community College conservation professor Bruce Gilman and his students have confirmed what scientists know about the mussels' life-cycle, reinforcing their belief that the foam is related to many mussels dying around the same time.
Olvany said he doesn't know whether the five- to six-year cycle of die-offs and increased foam would continue. For now, he stressed that the foam is a natural, relatively benign phenomenon.
"It's not a health threat," he said. "It's just a part of the ecosystem at this point."
Hilary Smith can be reached at (585) 394-0770, Ext. 343, or at firstname.lastname@example.org.