August 3, 2022

NJDEP Has Issued Alert About Harmful Algal Bloom in Lake

To the Editor:

Residents who use the D&R Canal State Park pathways along Lake Carnegie in Princeton should know that last week the New Jersey Department of Environmental Protection (NJDEP) issued an alert that a harmful algal bloom (HAB) that had been identified in the lake. The alert is at the “advisory” level which recommends that people and pets do not make direct contact with the water.

The alert was prompted by a local resident who contacted The Watershed Institute to report her concerns about the lake. We advised her to upload photographs of the water that she had taken to NJDEP’s online HAB reporting tool, which triggered testing of the lake and the subsequent issuance of an alert. Our StreamWatch volunteers also detected the presence of bacteria as part of the weekly sampling they do in waterways across our region.

HABs are commonly caused by phytoplankton known as cyanobacteria that use sunlight to create food. A combination of hot weather, nutrients from fertilizers, pet waste and other sources create conditions where cyanobacteria  grow too rapidly, producing toxins that are harmful to people and pets.

HABs could become a chronic problem without better controls on the use of lawn fertilizers, septic leaks, polluted stormwater runoff, and other contaminants flowing into the waterways. While we cannot immediately change the rising global temperatures that fuel the bloom growth, we can reduce the polluted stormwater runoff that carries bloom-inducing contaminants.

If you live along a stream, you can help by planting a buffer of native plants along the edge to filter out pollutants. Reduce or eliminate the use of fertilizers on your lawn. Add a rain garden or plant trees to reduce the amount of stormwater flowing directly into our waterways. If you would like to learn more, visit  the “Exploring Green Infrastructure” section on The Watershed Institute’s website (

If you would like to learn more about HABs and track current alerts, visit

Sophie Glovier
Assistant Policy Director
The Watershed Institute