Hawai'i's beaches were ranked sixth in the nation in beach-water quality, in a study released Tuesday by the Natural Resources Defense Council.

The report, "Testing the Waters: A Guide to Water Quality at Vacation Beaches," used data from water samples taken by the U.S. Environmental Protection Agency.

Hawai'i's samples came from Ala Moana Beach Park, Kuhio Beach, Magic Island Beach Park, the Royal-Moana beach, Sandy Beach and Hanauma Bay on O'ahu, Hanalei Beach, Po'ipu Beach and Salt Pond Beach Park on Kaua'i, and Wailea Beach on Maui.

The report said 2 percent of Hawai'i's samples exceeded national standards for pollutants.

It said 99 percent of Hawai'i beach-water pollution resulted from stormwater runoff and 1 percent from sewage.

Delaware was rated No. 1 in the study, with only 1 percent of its samples exceeding national standards. Storm-water runoff accounted for 100 percent of its beach-water pollution.

New Hampshire was second, Virginia third, Alaska fourth and North Carolina fifth.

"Pollution from dirty stormwater runoff and sewage overflows continues to make its way to our beaches. This not only makes swimmers sick — it hurts coastal economies," said Nancy Stoner, NRDC Water Program co-director.

The NRDC says that there were a cumulative 20,341 days in which ocean, bay and Great Lakes beaches were closed or the subject of health advisories. While that was down from 2007, it was the fourth consecutive year in which closures topped 20,000 days.

Rain plays a big role in flushing pollutants into the oceans, but last year it was relatively dry in California, Hawai'i and from Delaware to the southeastern states and the Gulf of Mexico.