Boston-area beaches have the best (and worst) water quality, according to a new report

Where are the safest beaches in the Boston area? A new report provides answers.

Local nonprofit Save the Harbor/Save the Bay released its annual “Beach Season Water Quality Report Card” on Monday, which assigns various beach water quality safety ratings from zero to 100% based on data from the previous year. The results are based on data from the Department of Environmental Protection and Recreation.

Pleasure Bay and City Point beaches, both located in South Boston, continued to receive the highest ratings. The nonprofit called South Boston’s beaches “the cleanest urban beaches in the country.” Both Pleasure Bay and City Point achieved 100% ratings for the 2023 season, continuing a trend of excellent ratings dating back five years.

At the other end of the spectrum is King’s Beach in Lynn, which has a rating of 55% for the 2023 season. This is the lowest score achieved by any of the 15 beaches included in the report.

“King’s Beach is a rarity in the Boston area,” Save the Harbor Executive Director Chris Mancini said in a statement. “This is a difficult and complex infrastructure challenge that has required dozens of meetings between stakeholders at every level of the community and government. “We are very fortunate to have such a committed, collaborative group from Lynn, Swampscott, the state and the federal government focused on trying to turn this beach around.”

Tenean Beach in Dorchester had the second lowest score, 73%. The largest declines in beach safety from 2022 to 2023 occurred at King’s Beach and Malibu Beach in Dorchester. Both results dropped by 19%.

Officials cited last summer’s record rainfall as the main factor influencing the 2023 results. Heavy rainfall can cause sewers to overflow and sewage from streets to flow into beach waters. This causes bacteria levels to increase, making beaches unsafe. Harmful algal blooms are also closing many beaches throughout the summer.

State officials regularly check water quality at beaches around Massachusetts, temporarily closing those that pose an undue risk to residents. Ten beaches across the state were closed Tuesday morning. The Department of Public Health maintains an interactive dashboard of all beach closures that is updated twice daily.

Officials separate water samples into water samples collected at freshwater beaches and those collected at marine beaches. According to the MDPH report in 2023, approximately 8% and 5.6% of samples collected from marine and freshwater beaches, respectively, exceeded bacterial water quality standards.

“Although exceedances were above average in 2023, the overall low historical exceedance rates indicate that Massachusetts beaches have generally high water quality,” the report authors wrote.

However, 2023 was the rainiest summer in the Boston area since 1955, according to a Save the Harbor report. As a result, the overall water quality safety rating for Boston Harbor beaches in 2023 was 85%, down from the previous score of 93%.

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