Stonington — Last week, some Old Mystic residents erected a hand-painted blue and yellow sign reading “Caution: Drowning Hazard,” and hung red “danger” tape along the edge of Haley’s Way Playground.

Less than 50 feet from the playscape at the town recreational facility known locally as the Old Mystic Playground, a 20,000-square-foot basin designed to capture storm water has turned into a large pond. There is no barrier between the two.

“Having lived here for 45 years, I know that when we get heavy rain, I get water pooling in my front yard. This land is lower than my land and they’re digging a hole another 2 or 3 feet down, so I knew we’d get water,” said neighbor Bob Haberman on Thursday while overlooking the approximately 1- to 2-foot-deep pool of water.

Neighbors at the playground Thursday afternoon said Coast Development Group of Newport, R.I., dug the compensatory storage basin the size of a youth soccer field behind 16 Smith St. on Jan. 2. It is part of a controversial plan to build a 4,000-square-foot house there and it has been full of water ever since.

A compensatory storage basin is a designated area on a property intended to contain excess water during periods of heavy rainfall.

Residents and local environmentalists have long opposed the plan, saying Old Mystic contains the largest inland, freshwater marsh in southeastern Connecticut which is crucial in preventing widespread flooding in the village. They said it also filters groundwater that drains into the Mystic River and provides habitat for birds and wildlife.

The northern part of that wetland extends up into properties on the south side of Smith Street, where 16 Smith St. is located.

The Inland Wetland and Watercourses Commission approved a permit for site work in February 2023 after soil scientists and environmental experts testified on behalf of opponents that wetland boundaries in the area extend farther than town maps show. The experts also said that planned tree removal could damage the adjacent wetlands and cause groundwater levels to rise, which could contaminate groundwater and increase flooding.

Under state law, the commission says the issue of flooding is not within its scope.

Haberman said he opposed the project from the start, and provided The Day with a February 2023 letter he said he sent to the planning department, selectman’s office and town attorney, citing the potential for water to pool on the property and create a safety risk.

“My concern, when I saw that, was not so much the argument with the wetlands. We have a playground here with children, and over here we have this huge body of water that an unattended child could walk away—parents being distracted—go into this pool and drown,” Haberman said.

A year later, he said his prediction has come true, and he was surprised by the lack of action by the town to somehow cordon off the area despite knowing about the issue for more than a week.

A Jan. 4 email from Smith Street resident Jonathan Fontanella to Candace Palmer, town inland wetlands and zoning official, contained photos of standing water on much of the property as well as the deeper, water-filled pit.

Palmer had no comment when reached by phone Friday.

It is unclear whether the neighbors contacted anyone else in the town about the issue.

On Friday, First Selectman Danielle Chesebrough said she had spoken with Palmer and planning department staff about the water and was told the situation is temporary. She said the water level is expected to drop as the ground dries out from recent heavy precipitation, and when work on the property is completed, the problem should not reoccur.

In the meantime, Chesebrough said the town is keeping an eye on the situation, and if the standing water persists, the town will take action to mitigate any risks to public safety.

Fontanella said Friday that the problem should never have been permitted in the first place, but a loophole in town regulations allowed it.

He explained that developers can skirt regulations against building in a floodplain by raising the ground level beneath a planned building and digging an equal sized hole to capture storm water, a compensatory storage basin.

“The biggest risk to increased flooding in Stonington is construction in the floodplain. Buildings and paved areas have measurable impacts that are much further reaching than you might expect,” he said, adding that when land is graded and vegetation is removed, the risk is exacerbated.

He said he is advocating for the town to amend zoning regulations to allow homeowners to continue to make repairs and improvements to their private property but prohibit development in a floodplain completely.

He postulated that by increasing the town’s Federal Emergency Management Agency community rating by just one point through more strict regulations, residents could see a 20% reduction to their insurance rates, but if the town does not take the issue seriously, it is at risk of losing National Flood Insurance Program support.

“And then there will be no way for us to rebuild when the next storm comes,” he said.