Bacteria has closed these Boise ponds repeatedly. Officials think they’ve found a fix.

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In the two years since Esther Simplot Park opened, its ponds haven’t made it through a swimming season without being shuttered for unhealthy levels of bacteria.

This year, Boise Parks and Recreation officials believe they’ve gotten ahead of the problem by adding a high-tech solution to an existing ban on dogs.

According to Parks and Rec director Doug Holloway, the department started on its project last fall, when it contracted with HDR Engineering to create what’s called “pond hydraulic modeling.” Essentially, the project diverts water from the Boise River into Quinn’s Pond, the easternmost body of water in the park system, which also has been closed in recent years due to toxic algae blooms and high levels of E. coli.

Currently there’s a small amount of water flowing into the ponds from the river, but Holloway said the model “increases that amount significantly.”

The model works by flushing fresh water through a 24-inch pipe that connects the river and the northeast corner of Quinn’s Pond at about 5 cubic feet per second, Holloway said. Water then moves from Quinn’s Pond into Esther Simplot Pond 1 through an 18-inch pipe as well as the side channel that connects the two bodies of water. From Esther Simplot Pond 1, the fresh water can flow into Esther Simplot Pond 2, where it will return to the river via a side channel near Veterans Memorial Pond.

Holloway said construction on the setup should be complete within a week or so, just in time for the March 15 through October 15 swimming season.

Alongside the infusion of fresh water, Parks and Rec is installing additional water aerators into the system, Holloway said. The department purchased and installed $50,000 worth of aerators last summer.

“Installation of more aerators throughout the three ponds should assist in preventing thermal stratification of the ponds which will aid in preventing algae blooms during the recreation season,” Holloway said in an email. “The aerators provide vertical mixing of the water keeping temperatures more consistent through the depths of the ponds.”

Parks and Rec is still weighing how many aerators it will install and where before the devices are introduced in May.

For now, Holloway said, the project is fairly experimental — the city is renting the river water that will flush the pond system, though it will try to secure permanent water rights if the effort proves successful.

He said he’s heartened by the improvements to the water quality since enforcing the ban on dogs, installing aerators and creating French drains around the ponds.

“E. coli continues to be present but we didn’t exceed unacceptable levels last year, which is a great indication that the remedies we have in place have been effective,” Holloway said.

The city is limited in how much cold water it can let into the Esther Simplot system — Simplot herself told the Statesman in 2016 that she wanted the ponds to maintain a temperature that’s pleasant for swimming in. Holloway said additional river water shouldn’t be an issue.

“It will be a balancing act to keep the temperatures comfortable while moving water through the ponds,” Holloway said. “We believe it’s highly doable to accomplish that. Most of the issues with bacteria and algae occur during the hottest times of the year. Any cooling of the water would be negligible during those warmer temperatures.”

Parks and Rec will continue to uphold the ban on dogs in both parks — though Fido can accompany you on the adjacent Greenbelt — and work with a contractor who “makes the geese feel uncomfortable.”

“The key source for the E. coli bacteria (two summers ago) was determined to be from dogs first and geese next,” Holloway said.

Beginning this spring, dogs also will be banned from the nearby Veterans Memorial Pond to avoid introducing additional bacteria to the system. (“Dog Island” is in the works at Ann Morrison Park, where it should be completed by early May.)

“Our number one priority is the safety of our users, and we are confident these new endeavors will create a safe environment for our customers,” Holloway said. “Coupled with the implementation of our previous efforts, the results of the pilot should provide for a safe and awesome recreational experience.”

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Nicole Blanchard is the Idaho Statesman’s outdoors reporter. She grew up in Idaho, graduated from Idaho State University and Northwestern University and frequents the trails around Boise as much as she can.