Update June 6, 2018:

On Thursday and Friday June 7 and 8, 2018, MWRA will be applying another alum treatment at the Chestnut Hill Reservoir in an attempt to prevent future algal blooms this summer.

Update May 10, 2018:

On Friday, May 11th, we will begin treatment of the algae bloom with alum. For a few days, the water may actually look worse before it looks better.

Update May 7, 2018

Water quality tests confirm that an algae bloom is in progress at the Chestnut Hill Reservoir. MWRA is working with the Mass. Department of Public Health and will be posting signs today at five locations that represent the main access points to the reservoir. The primary concerns are dogs swimming in the reservoir and fishing. Later this week, a contractor will take additional samples in preparation for a treatment of the reservoir next week.   

Please keep pets away from the water until further notice. We will continue to provide updates as the situation unfolds.

May 4, 2018

MWRA has been refilling the Chestnut Hill Reservoir following the annual winter drawn down to control invasive plants. Because of the exposed shoreline and some large rain and wind events, the reservoir has been discolored and brown, and sampling indicates an algae bloom is underway.

MWRA is in the process of taking water quality samples that will be analyzed by an independent lab. When those results are back early next week, we will determine what if any action is required and post the update here. The Chestnut Hill Reservoir is an emergency back-up reservoir and is not part of the active water supply system.