Robert Brown, a water resource specialist for the Minneapolis Park and Recreation Board, tested the water at Webber Park Pool earlier in the month. (Star Tribune/The Minnesota Star Tribune)

The ducks are to blame for the water problems at Webber Park pool in north Minneapolis, which was closed Tuesday for the 15th day this summer after failing another quality test.

"We're frustrated, obviously," said Jeremy Barrick, assistant superintendent for environmental stewardship. "We're working really hard to figure this out."

It appears that the ducks are swimming — and depositing fecal matter — in the holding pond during the day and in the swimming pools at night and overtaxing the natural filtration system, Barrick said. "We feel like the wildlife is the key," he said.

On the Park Board website announcing Tuesday's closing, there was an indication that something is being done. "New site changes recommended by the pool's designer are being put into place," the site said.

Those changes include adding predator decoys to try to deter ducks from landing in the pools, including coyotes and more owls. Barrick said they're looking at putting some sort of netting over the holding pond and buying temporary fountains to set up at night and disturb the pool surface.

Most swimming pools are cleaned with chlorine. The 500,000 gallons of water from the Webber pool get run through an adjacent pond where some 7,000 aquatic plants are supposed to scrub the water. The daily water tests screen for fecal matter and excess sediment.

The three-year-old, $7 million Webber pool was the first of its kind in the country. Last year, the pool was closed only six days for the whole season.

Typically, natural filtration pool systems take five years to mature, Barrick said. He noted the pool is in its fourth season and the intrepid urban ducks may have grown accustomed to the deterrents in place, such as sparkly materials, a single owl and the alligator heads.

"We're looking for humane ways to deter the wildlife," Barrick said.

Barrick said park staff has shared their meticulous records with the pool's designers, and weather conditions and cleaning protocols aren't the problem.

Park Commissioner Kale Severson said he has encouraged constituents to visit the North Commons pool, but unlike the pool at Webber Park, there is a charge to use that facility. Compounding the problem in Severson's district is the closure of the wading pool at Folwell Park because of leaks and the shuttering of the splash pad at the North Mississippi Regional Park.

Severson said he's heard from many constituents who are unhappy about the situation. "They have every right to be upset, I get it," he said. "It's a great swimming pool, it's a great asset. We just need to find a way to keep it open."

Chlorine isn't an option — yet. "It's been suggested," Barrick said ruefully. "As tempting as it is, we want to keep this as a unique facility."

Before the pool ever opened, there were problems with ducks and toads dirtying the cleansing pond. The price climbed to $7 million from the initial estimate of $4 million.

Park spokeswoman Robin Smothers said the 15 days of closures doesn't account for the days when one of the pools was closed. Last week the shallow pool, the one with the zero-depth entry for toddlers and non-swimmers, was closed for a few days while the deeper pool for diving and lap swimming was open.

Rochelle Olson • 612-673-1747 Twitter: @rochelleolson