Beginning in 1931, Kezar Lake suffered several decades of phosphorus overload, caused by the Town of New London routinely expelling nutrients from its wastewater treatment plant into Lyon Brook, the main tributary t Po Kezar. This pollution was carried miles down the brook into the lake. This went undetected until 1961 when periodic algae blooms began to harm the lake. 

Phosphorous, a nutrient-rich fertilizer, caused cyanobacteria to flourish, which in turn led to a lack of oxygen in the lake. Wildlife suffered as the water turned nearly opaque during the hottest days of the summer.


Shoreland owners, the public who used the lake, the state beach, hotels and restaurants were adversely affected by the dramatic decrease in water quality. Lakeside property values were reassessed.

 In 1971, concerned lake lovers formed the Kezar Lake Protective Association, and KLPA sought assistance from the NH Water Supply and Pollution Control Commission, now the Department of Environmental Services (DES).  Testing of potential sources of phosphorus loading, including from home septic systems around the lake, pointed indisputably to Lyon Brook as the source of the major phosphorus influx. The Town of New London’s management of its septic waste was identified as the problem. Shoreland owners took New London to court on two occasions to correct the problems, pay for clean-up and address property value losses. One result was that New London decomissioned its wastewater treatment plant in 1981.

The federal Clean Water Act was used to address Kezar’s problems through help by the federal Environmental Protection Agency and NH DES. Research and experiments were undertaken, led by Jody Connor, a limnologist with NH DES.

Through a period of trial and error, water quality began to improve following aluminum salt treatments. When injected into the lake, aluminum elements adhered to phosphorus particles and sank them to the bottom of the lake. Moreover, Chadwick Meadows, near the point where Lyon Brook enters Sutton, was planted with wild rice to absorb phosphorus, as part of a wetlands management strategy.

Kezar Lake is now healthy; nevertheless, KLPA remains diligent in its efforts to monitor the lake to avoid repeating its precarious past. KLPA’s mission is, among other things, to protect and enhance Kezar Lake by testing water quality,  educating the public on environmental best practices, and hiring lake hosts who monitor invasive species.


View DES's Amy Smagula's 2016 KLPA presentation:

Kezar Lake: From Good to Bad

and Back Again. A 70+ Year Retrospective


A memorial plaque to Jody Connor was placed by KLPA on the shore of Kezar Lake on Keyser Street. Jody dedicated many years to solving Kezar Lake's quality issues after a pollution crisis.