By Aaron Parseghian, WBZ-TV

The Head of the Charles Regatta, one of the premier rowing races in the world, will be held this weekend in Boston and Cambridge, Massachusetts. One concern ahead of the race appears to have been resolved. 

The Massachusetts Department of Public Health had issued a health advisory for a wide portion of the Charles, saying exposure to the water could be harmful to people and pets. The blooms, known scientifically as cyanobacteria, can produce toxins that cause skin irritation, gastrointestinal illness and even neurological effects.   

On Thursday, health officials provided an update that the course is no longer under an advisory after follow-up samples that were collected Tuesday tested at a safe level. The advisory remains in place for areas downstream, pending additional samples that will be taken next week.

Rower Andy O'Brien has been competing in the Head of the Charles for decades. But, while training this year, he noticed something different, widespread blooms of toxic blue-green algae coating parts of the river. The harmful bacteria had been there for weeks.

"It's usually down in the basin mostly," O'Brien said. "But this year, I mean, it just shot up the whole river and having one this late is so unusual." 

Marielena Lima, who monitors the river for the Charles River Watershed Association, said the bloom's persistence this year has been unusual. 

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

Recent nor'easter offers relief

However, the recent weather helped kill off some of the toxic algae.

"We are hopeful that the rain that we got the last few days and with the cooler weather that that'll give us the right conditions that we need to really finally break this cyanobacteria bloom," Lima told WBZ before news of the updated results. 

The Department of Public Health said recent testing showed bacteria levels dropping below safety thresholds at Magazine Beach and the Boston University Boathouse.

With the results showing further improvement and the advisory lifted for areas upstream of the Massachusetts Institute of Technology (MIT), the path is cleared for thousands of rowers descending on the Charles this weekend. 

"I would never drink the Charles water anyhow," O'Brien joked. "But I'm less tempted to do it now, for sure."