SANTA CRUZ -- Stinky water was seeping through thousands of Santa Cruz households' faucets, showerheads and washing machines Monday, but city officials say the problem, which stems from algae blooming in the Loch Lomond Reservoir, was not a health hazard.

Bill Kocher, director of the Santa Cruz City Water Department, said a city treatment plant operator noticed an unpleasant odor in the water on Saturday, when residents began picking up their first whiff of the "musty or earthy" scent.

On Sunday, workers tracked the problem to the Loch Lomond Reservoir, where they found algae blossoming. By then, the smelly water was already in the city's storage reservoirs, which feed some 34,000 households or about 90,000 people in the areas of Santa Cruz, Live Oak and Capitola, Kocher said.

He emphasized that the water does not pose a health risk, saying city officials know this because they continuously check the water for quality.

"We're simply overboard on testing for quality," he said. "Taste and odor is a secondary standard. It doesn't have anything to do with health, but it has to do with people's perception of water quality."

The water department has received several calls from residents who worry about the safety of their water, Kocher said.

The city shut off the supply from the Loch Lomond Reservoir on Sunday, substituting for the loss by extracting more water from the San Lorenzo River and North Coast springs.

The tap water lines should be cleared out by Thursday or Friday, Kocher said. Until then, residents could refrigerate the water before using it to help ease the smell and improve the taste, he said.

"It will pass. It will diminish over time," he said. "Some people will not even notice it because it didn't necessarily get in everywhere."

The Loch Lomond Reservoir provides only about 20 percent of the city's annual water demand, yet Kocher said the algae's odor is so strong, it has the potential to penetrate a good deal of the water supply.

"It's a persistent, nasty little bugger," he said.

Santa Cruz last dealt with a water odor problem in September 2004, Kocher said. He added that most of the time the city is able to predict when a reservoir is about to get a little stinky and switch water source before the smell leaks into the tap water. This time, however, the algae that cropped up were of a different kind than the blue-green algae city officials typically see in the Loch Lomond Reservoir, Kocher said. He did not know the name of the latest algae.