ADDISON COUNTY — County residents concerned about blue algae blooms in swimming areas may check with a Department of Health website to determine if they might be at risk.
There were two blue algae blooms in Lake Champlain off county towns last week, both of which Department of Conservation Watershed Management Division officials determined to be “low alert” events.
One was on July 8 near Tri-Town Road in Addison, and the other on July 10 in North Harbor in Ferrisburgh, just north of Basin Harbor.  
According to the Department of Health, in the case of a low alert event, “This area is open for recreation, but caution is advised in any location where dense accumulations or scums are apparent.”
Information on blooms may be found here at the health department’s tracking site: apps.health.vermont.gov/vttracking/cyanobacteria/2019/d/index.html.
The technical name for blue-green algae is cyanobacteria, which are naturally found in ponds and lakes. But according to vermont.gov, “under certain conditions, cyanobacteria multiply quickly, creating blooms. Some blooms produce toxins that can make people and pets sick.” According to the website, those conditions especially include concentrations of nutrients — and pollutants — such as phosphorous and nitrogen, plus warm summer water.   
The blooms have most often occurred in Lake Champlain’s less open northern areas, including such areas as St. Albans and Missisquoi bays.
Watershed management aquatic biologist Angela Shambault said this year has been typical for blue algae blooms. After a slow start because of the cold spring, the hotter weather and the runoff due to all the rain has created conditions for an average number of blooms, usually marked by green water and scum.
Often they vanish as quickly as they appear, but they can have serious health effects: Shambault acknowledged two dogs did die after swimming in a bloom in a private pond earlier this year, and she advised pet owners as well as swimmers to be cautious.