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Massachusetts Water Resources Authority

Updated: February 3, 2016
Original Post: October 27, 2015

CONTACT: Ria Convery, MWRA

MWRA to Temporarily Lower Water Level at Chestnut Hill Reservoir for Invasive Plant Control

MWRA - "Drawdown/Freeze-Off" of Eurasian watermilfoil

"Drawdown/freeze-off" method of naturally curbing Eurasian milfoil at Chestnut Hill Reservoir

UPDATE (02/04/16):

The refilling of the Chestnut Hill Reservoir began on February 3, 2016. The reservoir should return to a normal level within approximately three weeks.


Local residents and visitors walking the perimeter path of the Chestnut Hill Reservoir will notice a bit more exposed shoreline this in the coming months.

MWRA will perform a drawdown of the reservoir, lowering the water to 5 feet below normal elevation in order to control the growth of aquatic invasive plants.

A slow drawdown will begin on November 2, with the goal of reaching the target elevation by November 30. MWRA will monitor the response of the exposed areas to drawdown and, once it has been determined that a successful depth freeze has occurred, the water level will be restored.

The timing of water level restoration depends on temperatures and snowfall, but will likely occur in January. The MWRA drawdown plan allows for the pre-hibernation migration of amphibians.


The Chestnut Hill Reservoir, bordered by the cities of Boston and Newton, was built in 1870. It holds 500 million gallons of water and is an integral part of the MWRA’s emergency back-up water supply system. The dam receives a detailed regulatory inspection every two years and, with MWRA’s Capital and routine maintenance, continues to be classified as Satisfactory by the MA Office of Dam Safety.

Eurasian Watermilfoil

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Posted February 4, 2016