While the lake is a pastoral setting - on its shores are trails, stone benches, and a lighted fountain - beneath the surface, it is in a perennial battle.
Over the years, a buildup of silt and other contaminants from densely populated communities upstream has settled in part of the lake, depleting oxygen levels and threatening aquatic life and vegetation, said Borough Manager Dawn Marie Human. Last month, about 50 minnows died from low oxygen levels, she said.
"Dredging needs to happen on a repeated basis," Human said.
The borough received a $75,000 Delaware County grant to offset the $86,000 cost of the first phase of dredging. The money came from Marcellus Shale impact fees.
The initial estimate on trapping the turtles started at about $11,000, Human said.
The Eastern red-bellied turtles likely came to the lake through the Little Crum Creek, which feeds into Crum Creek and then the Delaware River. It is close to Darby Creek, where the reptiles often can be seen basking on logs.
Two turtles were spotted during the initial habitat assessment at the Ridley Park lake, said Marlin Corn, a herpetologist with Ecological Associates, the company hired for the assessment, a prerequisite for dredging.
A large female red-bellied turtle that was caught in the first week has been temporarily moved to a facility in Berks County for safekeeping until it can be released into the lake after dredging, Corn said.
The other red-bellied turtle is believed to have moved on, Corn said.
The traps also snagged some of the other reptiles that call the lake home.
A number of snapping turtles - common musk turtles, Eastern painted turtles, and red-eared sliders - some of which were "real monsters," were caught, said Corn. All but the red-eared sliders were relocated along Crum Creek, where, over time, they may make their way back to Ridley Park, he said.
The red-eared sliders were euthanized.
"Once they are captured and removed, it is illegal to release them," Corn said. The reptile is an invasive species often bought as a pet, then released by owners. The slider competes with native turtles for food and habitat, Corn said.
Bull frogs, sunfish, and catfish also found their way into the traps. They were released immediately.
The red-bellied turtle has been on the Pennsylvania list of threatened species since 1978. It is found around the Tinicum wetlands in Delaware County and Philadelphia, and a small group has made a home in Bucks County. Development has destroyed much of its habitat.
"There is a really good population at the John Heinz Wildlife Refuge" numbering in the hundreds, said refuge manager Gary Stolz.
Anne Bower, an associate professor of biology at Philadelphia University, has studied the red-bellied turtles at Heinz. She attached transmitters to about 15 of them and followed them for two to three years.
"They need a much bigger distance than people originally thought in terms of territory," Bower said. The reptiles can be found in the wetlands during spring nesting and have other favorite hangouts during the summer. During thunderstorms, the turtles go up and down the creeks, riding the tidal waves, she said.
If the borough gets more funding, it will attempt a $200,000 improvement project that would include planting native vegetation at the water's edge and an artificial floating wetland that will help curtail pollutants, said Charles Catania, borough engineer.
Having the turtle at the lake is a mixed blessing, Human said. She jokes that the borough is going to set up a fan club and sell T-shirts to celebrate the discovery and offset the costs.
But there was never any question that Ridley Park would help protect its imperiled residents.
"It is our little hidden jewel," Human said.
Contact Mari A. Schaefer at 610-313-8111, email@example.com or @MariSchaefer on Twitter.