SWAMPSCOTT — Last week’s torrential rainstorm sent bacteria levels soaring at King’s Beach, highlighting ongoing concerns about stormwater pollution and beach safety.

According to data collected by the DCR, the Eastern Avenue testing site measured 1,470 colony-forming units (CFU) of enterococci on Friday, June 19 — a data point about 14 times higher than the 104 CFU safe-swimming standard for Massachusetts beaches. 

Andrea Amour, founder of Save King’s Beach, said the elevated reading was consistent with what advocates typically see after major rainstorms.

“Anytime there’s a large amount of rain that’s going to flush out the storm drains, you want to avoid the beaches,” she said.

George Allen, a member of the Swampscott Board of Health who has long been involved in local water-quality monitoring efforts, agreed that major rain events typically cause bacteria spikes — though he acknowledged that the exact qualifications of a major downpour can be hard to define.

“It’s a combination of not only how much rain fell, but how fast it came down,” Allen said. 

Heavy downpours can flush bacteria, debris, and other contaminants that have accumulated in storm drains and drainage systems into local waterways. Allen pointed to Thursday’s storm, which dropped roughly 0.8 inches of rain in about half an hour, as an example of the type of event that can dramatically affect water quality. 

Amour said Save King’s Beach’s two primary public-health messages are straightforward: avoid swimming at beaches, particularly those with known pollution issues, for at least 24 to 48 hours after a significant rainstorm, and stay out of stormwater outfalls at all times. 

She urged beachgoers to avoid walking, wading, or allowing children to play in outfalls, where runoff enters the ocean. 

“The outfalls are the dirtiest parts of the beach,” Amour said. 

Recent data collected by engineering firm Kleinfelder illustrate Amour’s concern. Samples collected this spring from the Lynn and Swampscott culverts feeding Stacy’s Brook routinely measured bacteria levels in the thousands — including a May 28 sample in which both culverts exceeded 600,000 CFU. 

Those samples are collected before the water reaches the beach, providing a snapshot of conditions inside the drainage systems themselves. 

Allen said contaminants can accumulate in those systems between storms before being cleared out by rainfall. 

“The crud accumulates,” Allen said. “And when you get rain, it flushes it out.” 

King’s Beach presents a unique challenge because it spans the Lynn-Swampscott line. The DCR tests three locations along the Lynn side of the beach daily and uses a flag system to notify visitors when bacteria levels exceed safe limits. Blue flags indicate safe conditions, while red flags warn of elevated bacteria levels. 

The Swampscott Board of Health tests one location on its section of the beach on a weekly basis. Amour said she would like to see the town adopt a notification system similar to Lynn’s. 

“If you are entering King’s Beach from Swampscott and Lynn is closed, there is no indication,” she said. “I would like to see Swampscott adopt the same flagging system or have their bacterial warnings up at the same time that Lynn and the DCR have their red flags.” 

One complication, Amour said, is that test results are inherently delayed. Water samples must be processed in a laboratory for roughly 24 hours before results become available, meaning the numbers reported on any given day reflect conditions from the previous day’s water. 

To help residents navigate those delays, Save King’s Beach compiles publicly available testing data from the state’s beach water quality dashboard and presents it in a format that makes trends easier to track. 

Amour said daily testing conducted during last year’s UV pilot project revealed several instances where bacteria levels were unusually high on the Swampscott portion of King’s Beach, even when readings elsewhere were relatively low. That has prompted advocates and local officials to investigate whether buried stormwater outfalls on the Swampscott side could be contributing to the problem. 

“We would like to see the town seriously investigate those outfalls to understand if one or more of those is also contributing to the pollution at King’s Beach,” Amour said. “Because if they’re not, then that’s great. But if they are, we definitely need to button that up.” 

Save King’s Beach, now in its fifth year of advocacy, continues to work with local officials and volunteers to better understand the sources of contamination and push for long-term solutions. 

“When you have a big problem, you start to chip away at it by breaking it down into smaller pieces,” Amour said. “Because then they’re actually able to track and monitor their progress over time when they put millions of dollars of work into infrastructure. … I think it’s a good way for them to make individual progress on this.”