POULSBO — Three kids played on the shore of Liberty Bay Tuesday afternoon, splashing and twisting their faces at handfuls of muck.

“Ewwwww,” one 12-year-old said to the other.

On a bank above the beach, in the trees, older sister and aunt Kat Waag, 20, relaxed in the shade.

Waag said the kids have a standing order when playing on the beach: don’t get the water in your mouth. Down the shore 100 feet a metal sign warning people not to eat shellfish from the bay lied half-buried in mud.

“They’re nasty, they smell, they’re kind of gross,” she said of the beaches on Liberty Bay. “But it’s close and convenient,” she said, noting that the combination of beaches and shade keeps her family coming back.

To keep swimmers coming back, and especially shellfish harvesters, the Kitsap County Health District is embarking on a five-year, $666,000 project to identify, and reduce, the most notable pollutant in the water, fecal coliform bacteria.

“So they can have contact with the water and they don’t get sick, basically,” said Eva Crim, from the health district’s Pollution Identification and Correction Program, who is heading the effort.

The bacteria, most commonly found in excrement, is present in abundance in Liberty Bay, earning it an “impaired” designation from the state Department of Ecology. It can come from a variety of sources, failing septic and municipal sewer systems, pet and agricultural waste, boats, storm water runoff.

In fact, the bay is among the most polluted in the state, said Dave Garland, watershed unit supervisor for Ecology, which gave the health district $500,000 for the project.

“I would put it in the top third,” Garland said.

The project will have two health specialists trekking the shoreline of the bay, from Keyport in the southwest to Nesika Bay in the southeast, taking water samples of the streams and creeks that drain into the bay. Crim will begin the sampling Aug. 18. Using the results, the researchers will track the source of pollutants up stream, identifying “hot spots,” to locate the source of the pollution.

That’s half the project, the other half is working with property owners to help them fix and get the most life out of their septic systems, Crim said, noting that the emphasis is on helping people maintain their systems, rather than as the government enforcing regulations.

It also identifies every residence within 200 feet of surface water — on Liberty Bay and on the streams feeding the bay. District officials will pay a visit to the homes to hand out literature and inform the property owners of the project, and how they can help keep the bay free of pollution.

Stuart Whitford, program manager for the district’s pollution identification control program, said similar projects have been supported by neighbors. And although researchers can apply for search warrants if the owner of a property identified as a hot spot resists, Whitford said that hasn’t happened in Kitsap.

The bay isn’t monitored the way other nearby swimming areas are, like Wildcat, Buck and Island lakes, said Newton Morgan, environmental health specialist for the district.

This week, seven people fell ill after swimming in Wildcat and Long lakes, according to the health district.

He said it was OK to swim in the waters of Liberty Bay, “You just don’t want to drink it,” Morgan said, advising that after touching the water one should wash their hands.

The quality of water in Liberty Bay should not be confused with the quality of Poulsbo drinking water, which meets all federal and state requirements, according to June’s water quality report.