Fall is right around the corner. But until the leaves turn red and gold, people around Lake Champlain must contend with changing colors of a different sort: For the last two weeks, pea-green blooms of algae have been popping up in Missisquoi, St. Albans and Malletts bays.

“Mid-August through September is, unfortunately, what we in the business call ‘bloom season,’” says James Ehlers, executive director of the nonprofit Lake Champlain International.

Scientists have determined that early summer rain brings nutrients like phosphorus into the lake, and long stretches of sunlight facilitate photosynthesis, resulting in the pea-green film, Ehlers explains. 

“It’s not unlike April showers bring May flowers,” he says.

The unwanted nutrients come from a mix of agriculture and development. Environmental factors such as rain, wind, sunlight, sediment loading and depth can affect the distribution of the algae that is officially known as blue-green algae. But just what makes the St. Albans and Missisquoi bays more susceptible than spots further south isn't fully understood, Ehlers says. Sometimes areas with high nutrient concentrations report no blooms, while areas with lower concentrations end up getting them.

Last year, according to data collected by the Lake Champlain Basin Program, some the largest blooms in the lake were detected in the same spots they're growing this year. The exceptions are Burlington and Shelburne which, according to the Vermont Department of Health's tracking system, have been largely algae-free all summer. 

Pretty as the plumes of algae may look from the sky, Ehlers is emphatic about the public health hazard they present, noting residents along the lake who rely on that water for drinking should be concerned about contamination.

“For us this is more than just about the bugs and the bunnies. This is about the economic health of the region,” he says.