At the time of this writing, nearly 50 beaches in the Bay State are closed due to harmful bacteria and algae. The official term is “posted,” meaning marked with a “No Swimming” advisory sign, and the news comes as a major bummer in the swell of summer, with countless people having their plans spoiled as a result.
While the current state of the coastline is especially bad, beach closures are a familiar sight throughout Massachusetts at this time of year, as routine water quality monitoring frequently leads to limitations on swimming or water access.
But the process behind these decisions is rarely explained, leaving residents and visitors alike to wonder exactly what causes their local beach to get roped off. Some list reasons like “bacterial exceedance,” while a few just say “other.” Currently, two beaches in Worcester are off limits due to “harmful cyanobacteria bloom.”
Since June, an increasing number of towns and cities have seen their beaches shut down for different reasons and varying amounts of time. The incidents have spanned lake areas in MetroWest to ocean sands in Provincetown and Nantucket.
Many of the announcements have seemed sudden, especially in cases where the water looks clear to the human eye. But according to experts, the decision to close a beach is based on several layers of scrutiny, and is processed through multiple state and municipal departments.
The process of testing—and closing—Massachusetts beaches
Most beach closures occur in the summer, when local officials collect samples from prominent bodies of water. The process is intuitive, with examinations for indicators of bacterial contamination or other hazards that could pose a notable danger to swimmers.
Chloe Gotsis, the director of communications for the Massachusetts Department of Conservation and Recreation, explained that the department works alongside the water quality contractor TechLaw. Together, they conduct tests at swimming areas throughout the state park system. Water quality results are then reported to the Massachusetts Department of Public Health, where they are evaluated under the state’s public health regulations and standards.
According to the DCR, the commonwealth’s rec department tests beaches weekly, from the week right before Memorial Day through the end of the summer around Labor Day. Some highly trafficked beaches are tested more often, even daily. Per the agency, its water testing program is designed to “protect public health by identifying when bacteria levels indicate the water may be unsafe for swimming.”
Before the yellow warning tape comes out, TechLaw analysts scan water samples for bacteria. If levels exceed the acceptable DPH standards, those who are responsible locally post physical and online signs to prohibit swimming, and notify state health officials too. Massachusetts keeps an interactive dashboard that reflects the standing of beaches statewide.
A brief history of beach closures
According to state data, “of the 1,101 beaches operating in 2025, 184 (16.7%) posted no swimming signs on one or more days during the season. In total, there were a combined 3,345 posting days in 2025, with the majority of posting days due to the exceedance or expected exceedance (e.g., rainfall) of a water quality standard.”
Experts suggest that most beachgoers don’t realize or fully understand that elevated bacteria levels are oftentimes driven by environmental conditions, rather than a single source of contamination. Heavy rainfall, for example, can wash general pollutants and contaminants into lakes and ponds, carrying bacteria through stormwater runoff. Rainfall, however, is just one of many factors.
“Water quality can vary significantly from one beach to another,” Gotsis said. Adding that “due to localized environmental conditions,” there’s sometimes even variance between beaches in neighboring towns.
While changing weather is an influence, the overall number of beach closures has remained somewhat consistent in recent years. Omar Cabrera, the ethnic media relations and community health education manager for DPH, explained how an analysis of a busy two-week time period shows a nearly identical number of issues. Specifically, he pointed to a total of 34 closures during the second and third weeks of June 2024, compared with 33 during the same period in the following two years.
The danger of unsafe waters
While nearly all closures are temporary, Mass officials said they’re issued because even a small amount of exposure to contaminated water can pose significant health risks. They are done out of caution, even when that is a major inconvenience to beachgoers and tourists, to eliminate the possibility of illness or long-term health problems.
Cabrera said that swimming in unsafe waters may result in “gastrointestinal, respiratory, dermatological, eye and ear, and flu-like symptoms.” People with weakened immune systems are at an even greater risk for additional complications.
As weather patterns continue to get more unpredictable and environmental conditions fluctuate, public officials plan on increasing routine monitoring to determine when beaches are safe for swimming and public use. While some closures are frustrating and seem to come out of nowhere, they say the measures are designed to return bacteria levels to safe standards.
There is also a longer game. Looking past the current numbers, Cabrera emphasized how “climate change is expected to change rainfall patterns and increase flooding, which may increase pathogens in beach water and harmful Algal blooms.” Increases in water temperature, the community ed manager said, “will likely increase the growth and survivability of pathogens and the occurrence of harmful algal blooms.”
