Weekly Bacterial Testing

During the summer months when the bathing beach is open, the City of Newton complies with Massachusetts state regulations and tests the water weekly for E.coli. Crystal Lake is tested weekly for E. Coli. 

Samples are collected weekly, usually on Wednesdays. Results will be posted when available -- usually on Fridays.

Marine and freshwater beach guidance (MDPH)

2026 Bacterial Testing Results

*CFU stands for colony-forming units, the unit of measure used for samples like this.

General Information on Crystal Lake

Frequently Asked Questions 

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Cyanobacteria

Cyanobacteria, also known as blue-green algae, occurs naturally in freshwater. When conditions are right, cyanobacteria can multiply rapidly resulting in an algal bloom. There are many different types of algal blooms and some can be harmful to people and pets.

What does the City do if there is an algal bloom?

During the swimming season, staff routinely observe for signs of a cyanobacterial harmful algal bloom (cyanoHAB). If a cyanoHAB is visually identified, HHS follows the Massachusetts Department of Public Health (MDPH) guidelines and issues a public health advisory informing the public that the lake is unsafe for people and pets. An advisory is issued for the entire lake even if the algal bloom is only in one area because algae in any part of the lake affects the entire lake. Cyanobacteria are known to be highly mobile and move throughout the entire waterbody, even if they appear to us to only be in one area.

HHS coordinates with MDPH to test Crystal Lake to assess cyanobacterial levels. MDPH recommends lifting the public health advisory when there are 2 consecutive tests, one week apart, that are within recommended guidelines. The first test isn't collected until the bloom has visually disappeared from the water because cyanotoxin concentration is usually the highest when the water turns clear - testing while the bloom is still visible does not accurately capture the risk of cyanotoxins. Two tests are required because cyanobacteria cells release cyanotoxins into the water when they die. Algal toxins may be present when a visible scum or mat is no longer evident.

How does the City help prevent blooms?

The City of Newton performs water treatments that help reduce phosphorus levels, a key nutrient that promotes cyanobacterial growth. Application of alum and sodium aluminate is a well-established and common treatment for improving water quality without harm to local wildlife.

Newton performed water quality treatment on April 15-17, 2026. Newton undertook similar applications in 2020 and 2022 and monitors water quality and potential wildlife stressors in the months after each treatment. 

What causes cyanobacteria blooms?

As a kettle pond, Crystal Lake has no headwaters and is fed primarily through stormwater runoff. Stormwater runoff from impervious surfaces picks up leaf litter and organic debris which contribute to excessive nutrient levels such as phosphorus in local water bodies. When phosphorus levels are too high, blooms of harmful algae such as cyanobacteria can grow unchecked and cause negative health effects to swimmers and wildlife.