The dry-weather water quality of beaches in California hit a record high in 2007-08, but Los Angeles County had the worst overall beach water quality in the state for the third consecutive year, according to the Beach Report Card released by the Santa Monica-based environmental group Heal the Bay.

In its 18th annual Beach Report Card, Heal the Bay assigned A-to-F letter grades to 517 beaches along the California coast, based on levels of weekly bacterial pollution reported from April last year through March this year.

The Beach Report Card is a comprehensive evaluation of coastal water quality based on daily and weekly samples taken from sites along the entire coast of California, Heal the Bay explains. A poor grade means beachgoers face a higher risk of contracting illnesses such as stomach flu, ear infections, upper respiratory infections and skin rashes than swimmers at cleaner beaches.

During the high-traffic summer beachgoing season, 93 percent of beaches statewide received A or B grades, meaning very good to excellent water quality. That figure marks an eight-percent improvement over the previous summer.

Southern California’s record low rainfall last winter led to enhanced water quality by limiting the amount of polluted urban runoff that reaches the ocean via storm drain systems, Heal the Bay officials said. Only 29 of the beaches, or seven percent, monitored annually statewide received D or F grades in this year’s report.

“The state-funded California Clean Beach Initiative and local government action has led to significant dry-weather water quality improvement at many previously polluted beaches,” said Dr. Mark Gold, Heal the Bay president.

Heal the Bay officials noted that there continues to be a great divide between water quality in dry weather versus wet weather. This year 46 percent of monitoring locations statewide received fair-to-poor grades during wet weather, with 26 percent receiving failing grades. Wet weather grades were down slightly from the same period a year ago.

Los Angeles County had five of the ten lowest-rated beaches in the survey. The beach near the Santa Monica Pier ranked second in the list of the ten worst “Beach Bummers” in the state, trailing only Avalon Harbor Beach on Catalina Island.

While only 71 percent of Los Angeles County beaches received annual A or B grades, that figure marks significant improvement from last year. In the last Heal the Bay report, only 57 percent of Los Angeles County beaches earned A or B grades, and seven of its beaches were on the Beach Bummer list.

With the summer beachgoing season approaching, Gold noted that overall summer dry weather water quality at California beaches was excellent. Dry weather grades for Southern California beaches — San Diego to Santa Barbara counties — mirrored the statewide average for the first time in three years.

The growing disparity between improving dry grades and lagging wet grades indicates that cities and counties have made strides to mitigate dry weather pollution but are still grappling with stormwater runoff and the harmful effects it has on coastal water quality, Gold said.

“The report card is great news for the millions of people that visit California’s beaches each year,” said Gold. “But it also demonstrates that stormwater pollution was as bad this winter as it was a decade ago. Local governments have a long way to go before making beaches safe year-round.”

Los Angeles County received dramatically improved annual marks, with 71 percent of its beaches receiving a yearlong A or B grade, compared to 57 percent last year. But the county still had the worst overall water quality in the state, mostly due to severe water quality issues at numerous Long Beach locations, according to the report.

Meanwhile, 92 percent of Santa Monica Bay beaches (from Leo Carillo to Palos Verdes) received A or B grades during dry weather months, a dramatic improvement from the last two years.

One of the reasons that Los Angeles County lags in water quality is that its monitoring agencies collect samples directly in front of flowing storm drains and creeks, Heal the Bay officials said. Monitoring at these “point zero” locations, where polluted runoff often pools, is the best way to ensure that health risks to swimmers are captured in water quality data.

Most of the California coastline earned A grades throughout the year in dry weather. In the southern part of the state, Santa Barbara and Ventura counties went to the head of the class, with 100 percent of sites earning top marks. Beaches in Orange and San Diego counties earned annual dry grades of A or B at more than 95 percent of locations.

Information on the Beach Report Card,