Juniper Spencer, 3, paddles independently Thursday next to her mother, Lydia Powell, and her little brother, Julian, 1, at Lake Grove Park in Auburn. Lake Grove Park is the only public natural water swimming spot in Lewiston and Auburn. It reopened Thursday after closing for one day due to elevated E. coli levels. Regular testing ensures safety for public use. Andree Kehn/Sun Journal

AUBURN — The only public swimming hole in Lewiston and Auburn reopened for swimming Thursday, one day after it was closed due to failing a water quality test.

The outlet at Lake Grove Park, 2 Fair St. in Auburn, has been a popular spot this summer due to recent upgrades to the park and the availability of swimming.

However, a routine water quality test Wednesday exceeded the threshold for E. coli for the first time this year, causing staff to close the beach.

When it was tested again Thursday, city staff said results were “back within acceptable limits” and that the beach would reopen as soon as possible Thursday afternoon. Officials have said swimming has been “swim at your own risk,” with no lifeguards on duty.

Liz Allen, communications director for Auburn, said staff has been testing the water at Lake Grove Park, which is an outlet for Lake Auburn, for about five weeks. All the results so far this season have been well below the threshold — 250 parts per million for E. coli — that is considered a “negative” result, she said. The test is the freshwater drinking level standard for E. coli.

“This week’s negative result was not a particularly ‘extreme’ result, but instead was just a bit over the threshold,” Allen said. “We closed the beach in an abundance of caution, as the health and safety of our community is always our highest priority.”

In a post announcing the closure Wednesday, staff said there are numerous variables that can lead to the water quality decline, including summer heat and rainfall. The outlet has suffered from poor water quality in the past, causing officials to close the beach to public swimming for several years.

In the years since, staff has continually tested the water and had more consistent luck. But it also coincided with the addition of new playground equipment and watercraft, so even if swimming had to be paused, people could still be on the water.

Lake Auburn feeds the outlet through a single, 25-foot-wide outlet spillway under Route 4. Fresh water follows along an 8-foot-deep stream through the pond and runs out through a spillway into Bobbin Mill Brook, under Fair Street. Because it is relatively shallow, the water can at times be stagnant and susceptible to water quality issues due to factors like weather and wildlife.

Improvements made to the park in the last few years include new playground equipment, and the addition of kayaks and pedal boats. In July, city officials said the park had already seen “incredible” use by the public this summer as word has spread about the enhanced park.