Lake Massapoag Update

Lake Massapoag

Lake update August 23rd:

As of 8/23/2021 the lake has officially closed- which means that any swimming/water activities are “at your own risk” and there are no lifeguards on duty.  We have a Board of Health Meeting to discuss continuing the E-coli testing through “weather warm enough to swim”. Presently, E-Coli testing stops when the beaches close, as it only required while a beach is open by Mass DPH. The algae remains  day to day but will lessen as cooler weather comes in (algae likes nutrients (phosphorus and nitrogen), sunlight, warm water and shallow water. If you see anything that concerns you, please move down the beach and avoid the area for water activities.

Lake update August 21st:

Due to visible algae, the Veteran’s Memorial Park Beach will be closed for swimming today.

Lake update August 11th:

Per Sharon Recreation Department: Due to high levels of E-coli, the Community Center Beach will be closed for swimming for the remainder of the season. 

All season pass holders are welcome to use Veteran’s memorial Park Beach.

Kayaks and SUP may be launched at Community Center Beach

Lake update August 10th:

The Community Center Beach and boat launch are both closed as of 11 am today with visible algae. Veteran’s Memorial Beach remains open. Beach status remains day to day, as these blooms crop up quickly. The boat launch was clear at 9:30 am and had a bloom by 11 am- this will remain a dynamic situation for the rest of the summer. Thank you again for your patience and understanding with nature and our lake, as we continue to try and keep our residents safe.

UPDATE (8/6 at 12:40pm): Unfortunately, a suspected visible bloom has been observed at Community Center Beach. The beach is closed for swimming and will re-evaluate tomorrow morning.

August 6 update:

No visible algae has been observed, so both Veteran's Memorial Beach and Community Center Beach, as well as the boat launch, are open today.

Lake update August 4th:

Community Center beach is closed, as well as boat launch to stand one on Veteran’s Memorial Beach. This remains a dynamic situation. By late yesterday afternoon, all visible signs of harmful algae bloom had dissipated, but returned late this morning. Mass DPH beach Program continues to guide our actions and recommendations. PLEASE make sure to swim/ boat in areas with NO visible algae. The algae seems to be showing in the more shallow areas of the lake and none has been seen in the deeper regions.

Thank you for your ongoing patience

August 3 (afternoon) update:

Visible algae has now been noted by vigilant staff at Veteran’s Memorial beach and the boat launch- they will both be closed now and the situation monitored for the day. We will reassess opening tomorrow, based on visual surveillance today and tomorrow am. Please follow updates on town website and social media posts.

Thank you again for your patience as Mother Nature is proving to be unpredictable.

August 3 update:

Community Center beach is closed today for visible scum this morning. We will continue to evaluate day to day and post closings.

Thank you for your continued patience with keeping our town safe.

July 28 update:

The Massachusetts Department of Public Health (MDPH) collected water samples from locations on Lake Massapoag on Tuesday (7/27).  Cyanobacteria levels were 7,000 cells/ml at Memorial Park, and 6,800 cells/ml at the Community Center, which are below the MDPH guideline level of 70,000 cells/ml. The microcystin toxin level was <1 ppb for both samples. However, a visible surface scum of cyanobacteria was visible at the Community Center Beach during sampling.

Based on this information, MDPH recommends the following:

  • Lift the advisory at Memorial Park Beach and other access points on the northern half of the lake
  • Maintain the advisory at Community Center Beach and other access points to the southern portion of the lake while there continues to be visible cyanobacteria

What does this mean??

Veteran’s Memorial Park Beach and the boat ramp, EMS station for paddle boards and Massapoag Yacht Club - return to NORMAL operations!! Residents around those areas - enjoy your lake!

Community Center Beach will reopen on a day to day schedule - starting tomorrow. The beach will be surveyed each morning and throughout the day for any signs of algae bloom. If bloom is present in the AM, the beach will not open, or if a bloom becomes present throughout the day, the beach will be closed at that point.

How can we do this? Lake Massapoag is a large lake with many tributaries feeding water in and keeping the water moving and turning over. The water levels are monitored frequently and adjusted by Conservation to assist with keeping the water turnover. The southern aspect of the lake is prone to more issue, simply because of the shallow depth. Cyanobacteria like heat and sun to grow (along with nitrogen and phosphorus)- the shallow depth makes it warmer. We now have documented bacteria and toxin levels, with the presence of a small cyanobacteria surface scum, so we know that the lake is clearing the toxins well- that is why we are able to now go on a day by day basis. We will continue a testing schedule through DPH if any further algae blooms are noted.

As always, we thank you for your patience in helping to keep our community safe and healthy.

July 21 update:

The Massachusetts Department of Public Health (MDPH) collected water samples from locations on Lake Massapoag on Tuesday (7/20) – the Memorial Park Beach and the Community Center Beach. Cyanobacteria levels were 8,100 cells/ml at Memorial Park, and 6,900 cells/ml at the Community Center, which are below the MDPH guideline level of 70,000 cells/ml. The microcystin toxin level was <1 ppb for both samples.

MDPH requires two rounds of samples below the guideline level, one week apart, to rescind the advisory. These results will be considered the first low sample, and MDPH will sample again next Tuesday (7/27).

July 19 update:

Unfortunately, the algae bloom was visualized as a “scum mat” on one side of the lake and algae was noted on the opposite side of the lake as well- this was Thursday 7/15. The scum mat was noticed by astute Recreation Department staff and it was recommended to survey the lake for additional areas, which were found.

The Massachusetts Department of Public Health’s (MDPH) Environmental Toxins Program oversees the beaches for Massachusetts and issued an advisory on Thursday 7/15. The bloom continued to enlarge throughout the day on 7/15. Friday 7/16 saw it starting to dissipate and surveillance on Saturday 7/17 and Sunday 7/18 from shore and by boat for the entirety of the shore revealed no visible algae and resolution of the “scum mat”. MDPH has been very responsive to the Sharon Health Department’s phone calls/emails and detailed in their guidance. There are unfortunately many areas in the state dealing with this now, and being a natural occurrence, a strict timeline of events/occurrences can’t be predicted. Visual surveillance on a daily basis is no longer needed per MDPH, but if anything is noticed, we will report it.

The advisory from MDPH will remain in place until 2 water samplings (collected from different areas) are collected a week apart and the toxin levels are below their limits or no toxins are found. MDPH was encouraged that with multiple areas feeding the lake and water moving in/out that there will be no toxin levels present.

The testings are booked with a MDPH contractor for tomorrow (7/20) and next Tuesday (7/27), although the tests themselves are quick, it is usually a 24 hour turn-around from testing to being given the all clear and having the advisory lifted. An ESTIMATED timeline of Wednesday (7/28) afternoon at the earliest that the Advisory would be lifted.

The Town is following MDPH's recommendation to keep the lake closed to all activities and the Advisory remains in place until the testing confirmed absence of cyanobacteria.

Thank you for your continued patience.

July 15

A visible suspected cyanobacteria scum was just found and reported to the Massachusetts Environmental Toxicology program, which requires posting of no water activity signage and immediate closure of the lake. Please rinse off well at home as soon as possible.

The lake will remain closed until cleared by Mass DPH. Homeowners with lake access must also refrain from entering the water for any recreational activity.

Below are some resources to learn more about cyanobacterial blooms, including how they can be deadly for pets and livestock.

We will post updates as necessary. Thank you for your patience as we navigate this situation.

For general questions about cyanobacteria, contact the Massachusetts Department of Public Health at 617-624-5757 or visit

For questions about this advisory for the lake, please contact the Board of Health at 781-784-1500 x1206 or

algae sign