LOS ANGELES, May 24 (Xinhua) -- Seven best-known beaches in the Los Angeles County rank among California's 10 most polluted, according to an annual environmental report.

    For the second straight year, Los Angeles County had the worst coastal water quality in the state for the 12 months ending March 31, said the report by the environmental group Heal the Bay.

    Although record low rainfall made most of California's coastal waters safer to bathe in over the past year by reducing contaminated storm and creek runoff into the ocean, it wasn't enough to improve potentially risky bacteria levels at some of Los Angeles County's best known beaches, according to the report published by the Los Angeles Times on Thursday.

    The nonprofit group assesses daily and weekly fecal bacteria pollution from nearly 500 California beach sites from Humboldt County to the Mexican border, giving each a grade of A through F.

    Beaches rated F included Surfrider and Marie Canyon storm drain in Malibu, Santa Monica Municipal Pier area, Castle Rock in the Pacific Palisades area, and Avalon on Catalina Island.

    Higher bacteria counts raise the risk of contracting gastrointestinal ailments, ear infections, upper respiratory infections and skin rashes, and can also harm fish and wildlife.

    The biggest surprise in this year's report: the dramatic deterioration in water quality along the several-mile Long Beach coastline, which ranked worst in the state, said Mark Gold, president of Heal the Bay. Nearly all of the 25 beaches tested there received grades of C through F -- 14 of them Ds and Fs -- leading the environmental group to lump the city's beaches into a single entity.

    "It's a very dramatic change, as Long Beach historically has had excellent water quality," Gold said.