Waters off California's coast are cleaner in dry weather than they've been in years, according to an environmental report released Wednesday. The report also shows that Ventura County's beaches are the cleanest in Southern California.

The environmental group Heal the Bay's "Beach Report Card" analyzed 517 beaches on the California coast, ascribing them grades from A to F. The level of bacteria between April 2007 and March 2008 was taken into account.

As the findings reveal, water quality is improving statewide. However, Los Angeles County still has its seawater strained with bacteria. Other counties with bad water quality are the waters at Santa Monica Pier, Poche Beach and northern Doheny State Beach in southern Orange County, Marie Canyon at Puerco Beach in Malibu, Cabrillo Beach in San Pedro and some locations in Long Beach.

It seems the good condition of the waters was favoured by the large number of days with dry weather. Experts explained that when the weather is wet, rain washes polluted water down creeks, storm drains and into the ocean.

One of the indicators used in water tests is the ecal coliform (also known as E. coli), which can cause a range of infections and is more active on wet weather. But Mike Grimmer, Heal the Bay's Beach Report Card manager, said this is nothing unusual.

"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," he stated.