Chilmark Pond’s 2026 Monitoring Season

Pond Visits

 During the 2026 field season (May–October), Chilmark Pond Foundation’s science team visited the pond to conduct water quality monitoring on 22 days. This is the same number of sampling days as last year!

The science team out on Chilmark Pond lower basin collecting data

Water Quality Samples

During a standard sampling day, the science team travels by boat to 11 established monitoring stations throughout the Chilmark Pond ecosystem. At each station, a water sample is collected and analyzed to determine cyanobacteria concentrations. This year, the team collected 171 water quality samples, compared to 261 last year.

Why the difference? In mid-July, following a full sampling run, cyanobacteria concentrations were found to be extremely high throughout the lower pond, while the middle and upper pond reached the Orange Bloom Watch level. Following recommendations from the Boards of Health and out of an abundance of caution, the team shifted to collecting shoreline samples in the lower pond to minimize potential exposure to bloom conditions. Because some of the established monitoring stations were too far from shore to safely access, not all stations could be sampled during these visits.

Our final sampling run on October 27th marked an important milestone: for the first time since the bloom began in mid-July, no cyanobacteria were detected in our samples.

Cyanobacteria bloom in lower Chilmark Pond

Nutrient Samples

A total of 35 nutrient samples were collected from Chilmark Pond this year, compared to 48 last year. Nutrient samples are collected monthly throughout the field season to measure nitrogen and phosphorus levels in the pond.

In addition to the standard water quality measurements and samples collected during a regular field day, nutrient monitoring involves collecting water samples from mid-depth using a Van Dorn sampler. These samples are filtered and processed before being sent to the Marine Biological Laboratory in Woods Hole for further analysis.

Collecting a nutrient sample using a van dorn sampler.

Toxin Samples

This year, the science team collected 30 toxin samples from Chilmark Pond, six more than last year. These samples are sent to two laboratories for analysis: the U.S. Environmental Protection Agency (EPA) and Dr. Gobler’s laboratory at Stony Brook University.

Unlike our routine cyanobacteria monitoring, toxin sampling helps us determine whether a bloom is producing toxins that can pose risks to human and animal health. While results from the EPA's toxin analysis are not expected until the end of the year, these data will be an important part of understanding the potential health risks associated with cyanobacteria blooms. Over time, toxin results will also help us better understand patterns in bloom toxicity and assess the potential risks of future blooms in Chilmark Pond.