Harmful Algal Blooms Monitoring Program

The monitoring season for HABs has ended and will resume back in June. If water looks green or you are unsure if a HAB is occurring please use caution when recreating in or around the waterbody.

The Town of Nantucket, in collaboration with Nantucket Land Council, Nantucket Conservation Foundation, Nantucket Land Bank, Linda Loring Nature Foundation, UMASS Boston, and Mass Audubon monitors the following ponds for harmful algal blooms (HABs) weekly from June through October: Long, North Head of Long, Miacomet, Sesachacha, Capaum, Gibbs, Hummock, Clark’s Cove (West Hummock Pond), Maxcy, Washing, Tom Nevers, Stump, Almanac, Wigwam, Pout, and UMASS Boston’s Nantucket Field Station (NFS) Ponds.

Report algal bloom
Report algal bloom sp
As part of the Massachusetts Department of Public Health Bathing Beach Testing Program, the Town of Nantucket tests public beaches weekly during the warmer months to ensure bacteria-related water quality requirements are being met. This testing is different from toxic algae as it focuses on bacteria levels, thus sometimes posing an issue with conflicting Town signage. If the Health Department sign indicates water is safe for swimming but the water looks green, please use caution when recreating as potential toxins may be present even when bacterial levels are considered safe for swimming.  
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Adopt a Pond Program

Want to help expand our capacity to monitor all waterways on Nantucket? By “Adopting a Pond,” you can help us monitor water conditions by visiting https://www.nantucketbiodiversity.org/pondsurvey and downloading the Nantucket Pond Water Guide. Please contact Thaïs M. Fournier at tfournier@nantucket-ma.gov for more information on volunteering to monitor our ponds.

Algal Blooms Partners

HABS Occurrence in 2021


The Nantucket HAB monitoring team performs VISUAL HAB inspections for the above mentioned ponds. HAB sampling is only performed by the TON for Hummock, Long, Miacomet, and Sesachacha Ponds.

The duration of a HAB occurrence is dependent on a number of factors, including physical and biological conditions, and therefore is not possible to predict in advance.

As monitoring is performed weekly and at specific locations and times, blooms may occur and disappear throughout the week.

Not all algal blooms that occur in waterbodies are harmful. If you are unsure whether a bloom is harmful or not, please keep away from the pond.

For more information, please visit the Environmental Protection Agency website at https://www.epa.gov/cyanohabs.