Head of the Charles won’t be affected by bacteria bloom, officials say

The Head of the Charles Regatta is proceeding as planned this weekend despite a growing toxic algae bloom in the Charles River, health officials announced.

A cyanobacteria public health advisory along the Charles River has expanded to include all areas downstream of the Cambridge Street Bridge, according to an update released Thursday on Boston.gov.

However, officials said that the advisory has been lifted at both Magazine Beach and the BU DeWolfe Boathouse, where the regatta will take place.

Earlier this month, Boston health officials issued an emergency alert due to potentially harmful levels of cyanobacteria in the Charles River. The alert sparked concern over whether the bloom would impact the iconic race.

Officials expanded the advisory area after test results showed the toxin-producing algae were above safety thresholds in areas of the Charles River that are downstream from the 3-mile race course.

The regatta starting line is located at the Boston University DeWolfe Boathouse, and the finish line is near Christian A. Herter Park. Magazine Beach, near the start, is a spectator zone. About 12,000 rowers and 33,000 spectators are expected to attend the race.

The Centers for Disease Control and Prevention (CDC) warns that the blue-green algae can cause skin rashes and eye irritation upon contact. Swallowing contaminated water can lead to gastrointestinal issues, such as vomiting and diarrhea. Children and small pets are more vulnerable to serious symptoms due to their smaller body weights, health officials said.

City officials are asking people and pets to avoid the Charles River downstream of the Cambridge Street Bridge. Anyone who comes in contact with water in the advisory zone should rinse off immediately.

Morgan Rousseau is a freelance writer for Boston.com, where she reports on a variety of local and regional news.