Dangerous Algae Bloom Affects Charles River

The water in the Charles River isn't looking favorable for this weekend's Head of the Charles Regatta rowing race. 

Widespread blue-green algae blooms have significantly expanded along the Charles River, covering areas of the river previously unaffected by the algae growth.

"It's usually down in the basin mostly," said rower Andy O'Brien in a statement shared with WBZ-TV CBS News Boston. "But this year, I mean, it just shot up the whole river, and having one this late is so unusual."

The Massachusetts Department of Public Health has issued a health advisory warning that exposure to the cyanobacteria blooms could cause skin irritation, gastrointestinal issues, and neurological effects, affecting both people and pets.

Marielena Lima, who observes the river for the Charles River Watershed Association, said the algae bloom's prolonged presence this year has been out of the ordinary. 

"It started at the end of July, so it's been a pretty long bloom," she said in a statement to CBS News Boston. "We didn't expect it to expand even more this season, so that's definitely new."

Recent weather impacts, including a nor'easter over the Oct. 11-12 weekend and cooler temperatures, are expected to help reduce algae levels. Recent tests have shown that bacterial levels have dropped below safety thresholds at key locations, including Magazine Beach and the Boston University Boathouse.

If further testing confirms continued improvement, the health advisory could be lifted upstream of the Massachusetts Institute of Technology (MIT). This development would allow the race to proceed for thousands of rowers who will take to the Charles River for the Head of the Charles Regatta this weekend.