Algae Monitoring Program

Hobbs Brook




Algae are the backbone of a healthy aquatic environment. 

They produce oxygen, recycle nutrients from the water column, and form the basis of the aquatic food web. You have algae to thank for the air you breathe, fish you eat, and even the fuel in your car! However, when water quality becomes impacted by excessive nutrients, algal populations can swell to form blooms. These blooms of algae or cyanobacteria can impact the taste and odor of the drinking water, and occasionally produce harmful toxins. Due to a lack of excessive nutrient runoff and low residence times, Cambridge reservoirs are not at high risk for developing harmful algal blooms. However, it is still important to monitor for changes in the algal community, which could indicate the start of a harmful bloom.

In 2019, the Cambridge Water Department (CWD) developed an algae sampling program to identify, quantify, and monitor algal communities in the city’s drinking water supply. CWD staff collect water samples from Hobbs Brook, Stony Brook, and Fresh Pond Reservoirs and ship the samples to a contract laboratory for identification and enumeration. The CWD laboratory also has a microscope that can be used for in-house algae identification on an as-needed basis. Through the CWD algae monitoring program, taxa of phytoplankton in each sample are recorded to establish a baseline of the algal community. CWD staff also check for algae that can produce toxins. These data can be used to inform watershed management and water treatment operations and can serve as an indication of watershed health over time.

For more information about algae and the monitoring program at CWD, read the 2019 Algae Monitoring Report or visit the photo gallery to see pictures taken with the microscope of algae from the Cambridge watershed!

Sampling BottlesZooplankton