Overall failure rates drop, but high bacteria counts persist despite another dry monitoring season
For the second straight year, overall failure rates dropped in Save the Sound’s annual fecal indicator bacteria monitoring season. Of the 745 water samples collected by staff and volunteer community scientists from 66 locations from Greenwich, CT, through Westchester County and into Queens and Nassau County, NY, 58% failed to meet the state-established single sample safe swimming criteria. That’s an improvement of 2% from 2024 and 6% from 2023 but up 2% from 2021. The 12-year-old monitoring program hasn’t seen a season where less than half the overall samples failed since 2017 (43%).
The 2025 season had the highest frequency of dry weather samples in the western Long Island Sound since 2022. Only 16.5% of the samples were taken under wet weather conditions—which occur when a half-inch or more of rain is recorded in the 72 hours prior to sampling—down from 2024 (26.4%) and 2023 (46.3%). The 622 dry samples were the most ever collected by Save the Sound in a single monitoring season.
Only 46% of those passed, up 2% from both 2023 and 2024.
“While a year-over-year improvement in the overall failure rate is encouraging, of course, it’s important to recognize that more than half of the dry samples failed for the fifth time in six years,” said Peter Linderoth, director of healthy waters and lands for Save the Sound. “Dry weather failures in urbanized areas have been shown to be associated with leaks in sanitary sewer infrastructure.”
Dry weather samples tend to pass at a higher rate than wet weather samples. In wet weather, runoff flushes pollution off the landscape and into waterways, and occasionally can trigger a larger volume of untreated sewage being released instead of making its way to a sewage treatment plant.
That the 2025 season saw only a marginal improvement in overall failure rate can be attributed to a double-digit increase in wet weather fails. The failure rate (82%) was 11% higher than 2024 and is the highest in the program’s history. While fewer wet samples were collected, they tended to have high hits for fecal contamination.
Rivers remained the most polluted type of site sampled, failing 73% of the time. Samples collected at embayments failed 43% of the time, and those collected along the shoreline failed only 16%.
“Sewer lines are engineered to run from higher-elevation locations to lower ones wherever possible, using gravity to move wastewater to treatment plants. These pipes often run alongside or close to the rivers and streams that run through backyards, along school properties, and past playing fields across our communities,” said Linderoth. “These rivers at times carry dangerously high levels of pathogens from fecal contamination that have the potential to make people sick when they interact with those waterways.”
Only three locations went the entire 2025 monitoring season without a failing sample: Glen Island Park (New Rochelle, NY), Greenwich Cove (Greenwich, CT), and Indian Harbor Yacht Club (Greenwich, CT).
Thirteen sites, though, had all of their samples fail in 2025: Parsons Beach @ 233rd Street (Queens, NY), Mamaroneck Harbor East Basin (Mamaroneck Village, NY), Udalls Mill Pond (Saddle Rock, NY), Byram River @ Comley Avenue (Greenwich, CT), Beaver Swamp Brook @ Rye Neck High School (Mamaroneck Village, NY), Beaver Swamp Brook @ Greenwood Union Cemetery (Harrison, NY), Tributary to Beaver Swamp Brook (Harrison, NY), Glover Field (Mount Vernon, NY), Hutchinson River @ Migui Park (Mount Vernon, NY), Outfall @ Farrell and Beechwood (Mount Vernon, NY), Mamaroneck River @ Saxon Woods Park (Mamaroneck Town, NY), Mamaroneck River @ Saxon Woods Road (White Plains, NY), and Sheldrake River @ Columbus Park (Mamaroneck Village, NY).
Water samples from all locations are collected by Save the Sound full-time and seasonal staff and volunteer community scientists, trained by Save the Sound, once a week over the 12-week monitoring season. Those samples are delivered to the John and Daria Barry Foundation Water Quality Laboratory in Save the Sound’s Larchmont office, where our staff analyze them for the presence of fecal indicator bacteria: Enterococcus in marine water, E. coli in freshwater. Full results from the 2025 monitoring season and all previous seasons are available at SaveTheSound.org.
“I want to thank our seasonal staff, as well as the 16 community scientists who volunteered their time to work with us this season,” said Linderoth. “Thanks to their commitment and hard work, we were able to consistently conduct sampling at 66 locations.”
Volunteers interested in participating in the 2026 bacteria monitoring season should send an email to pollution@savethesound.org.