CONCORD, CALIF. — Standing on the edge of a murky swimming pool, public health worker Jeremy Tamargo scoops up a sample of brown water to ensure that the mosquito treatment he administered earlier is still working.
A collection of plastic toys stashed in a corner of the yard and a stuffed toy floating forlornly in the swampy water indicate that a family once played here, until foreclosure forced a move.
Now the once-sparkling turquoise jewel is a "green pool," a legacy of the foreclosure crisis -- and a breeding ground for millions of potentially disease-carrying mosquitoes that have kept health officials busy in California and elsewhere.
"It's always in places where you least expect it," said Tamargo, who is on the front lines of finding and treating abandoned pools in Contra Costa County's suburbs east of San Francisco, an area with large numbers of foreclosed homes. "Could be a $500,000-home neighborhood, could be a million-dollar home neighborhood, and in the backyard there's this."
Authorities can order owners to take care of properties, for instance by treating or draining pools. The problem is finding who's responsible for an empty house that may have been flipped more than once.
"If you're a building official or a zoning inspector for a local government, you really have to become almost like a CSI investigator just to track down who you should be talking to," said Joseph M. Schilling, director of policy and research for the National Vacant Properties Campaign, which focuses on the problem of abandoned houses.
"Nobody wants to take responsibility," Tamargo said. "I guess they figure because they're not living here or whatever, it's not their problem anymore. The banks -- this is probably the least of their worries."
So, for something that can't wait, like swampy pools, local officials fix the problem themselves and then try to seek reimbursement.
In an effort to force ownership of the problem, officials in Chula Vista passed an ordinance requiring that after recording a notice of default on a vacant property, lenders pay a $70 fee and hire a property management firm.
The ordinance has been in effect for more than a month, and so far there have been about 30 voluntary registrations. Notices of violation are being processed for another 30, said Doug Leeper, code enforcement officer.
Chula Vista, a city of about 175,000, has hundreds of homes in foreclosure, so for now, the city has been fixing what has to be fixed, "having to put the money up front we really don't have," Leeper said.
Efforts to quash murky pools got a boost earlier this year when Gov. Arnold Schwarzenegger declared a state of emergency, providing about $6 million for mosquito control, surveillance -- including flyovers to look for the telltale signs of oblong and kidney-shaped brown blotches -- and information campaigns urging neighbors to report neglected pools.
Statewide data on murky pools aren't available, but "we certainly recognize that the high number of foreclosures contributed to West Nile virus transmission in urban areas this year," said Vicki Kramer, chief of the California Department of Public Health's vector-borne disease section.
As of early November, there were more than 370 cases of West Nile virus reported in California and 16 related fatalities, four from Kern County, which had some of the highest foreclosure rates in the state.
The year-to-date total is higher than last year's of 278 cases and seven deaths, but is lower than officials had feared, said Kramer, who credited the emergency declaration with warding off a bigger outbreak.
Health officials say that earlier in the year it looked like the state was on pace to rival the totals posted in 2004-05 (around 800 cases both years), when the virus first hit the state, targeting susceptible populations.
About four out of five people who are infected with West Nile virus won't show any symptoms, which include fever, nausea, headache, and muscle aches. But in very rare cases -- about one in 150 -- patients will develop severe illness, including meningitis or encephalitis.
Murky pools meant a busy year for health officials.
In Contra Costa County, officials estimate they spent fewer than 1% of service calls on swimming pools last year, compared with having technicians spend up to half their time inspecting and treating pools this year, said Deborah Bass, public affairs manager for the Contra Costa Mosquito and Vector Control District.
It's not always easy to tell whether a pool has fallen victim to foreclosure or has been neglected for other reasons, but about half of those pools were confirmed as foreclosures, Bass said.
Officials elsewhere in the country have reported similar problems.
In the Southern Nevada Health District, home of Las Vegas, officials logged nearly 1,600 complaints of standing water, primarily murky pools, by early November, compared with just over 1,000 for 2006, said Vivek Raman, vector control program supervisor.