Ventura County's beaches are, as usual, the cleanest in Southern California, according a water-quality report released today.

The environmental group Heal the Bay's "Beach Report Card" assigned grades of A-F to 517 beaches on the California coast, based on levels of bacteria during testing from April 2007 to March 2008. All but one of the 56 Ventura County beaches rated an A when tested during the spring and summer months. The exception, Rincon Beach, got a B grade.

It was the second year in a row that Ventura County's beaches were the cleanest in the study.

"It's amazing how good the water quality is there (in Ventura County)," said Mike Grimmer, Heal the Bay's Beach Report Card manager.

The water isn't as clean after it rains, but it is still cleaner than the water at most Southern California beaches after a storm. Ocean water is dirtier in wet weather because the rain washes polluted water down creeks and storm drains and into the ocean.

During the winter months, the Ventura County Environmental Health Division only tests the water at 11 of the county's beaches. Heal the Bay gave all 11 an A in dry winter weather; in wet weather, there were six Cs, four Bs and one A.

The Cs were at Rincon Beach; Mandos Cove north of Ventura; Surfer's Point and Peninsula Beach, both in Ventura; Hollywood Beach at La Crescenta Street; and Channel Islands Harbor Beach Park at the south end of Victoria Avenue.

"In dry weather, the beaches are generally pretty good. In wet weather, all bets are off," said Paul Jenkin, a campaign coordinator for the Ventura County chapter of the Surfrider Foundation.

Jenkin lives in Ventura and surfs frequently at beaches in Ventura and Oxnard. He said he's gotten ear infections and other ailments from surfing after a rainstorm.

The bacteria in the water — much of it from human or animal feces — can cause a variety of infections and other health problems. That's why public health officials urge surfers and others to stay out of the water for 72 hours after a heavy rainfall.

Jenkin said he thinks that's a good idea, but it shouldn't have to be that way.

"It's clear that local governments can take actions to reduce the urban runoff," he said. "It really takes a change in the way business is done by public agencies. It takes going back and retrofitting the existing storm drain infrastructure. The drains have been designed to put it all in the ocean."

Grimmer said he's seeing improvement up and down the state every time Heal the Bay releases its report card. Statewide, 93 percent of beaches received A or B grades when tested last summer, an 8 percent improvement from the summer of 2006.

In wet weather, 46 percent of beaches were graded at C or worse.

"If you're at an open-ocean beach and it's dry weather, you have almost a 100 percent of swimming in clean water," Grimmer said. "We're making some strides on wet weather. ... Unless we live in a society where there's no trash anywhere, a lower standard is always going to be expected during wet weather conditions."