Hawaii beachgoers swam in some of the cleanest waters in the nation last year, according to the 21st annual beachwater quality report released today by the Natural Resources Defense Council. 

Only 3 percent of beachwater samples in Hawaii exceeded health standards in 2010, ranking the state as having the fourth cleanest beachwater in he nation last year. However, water quality ratings varied by island. While only 1 percent of Honolulu’s samples exceeded health standards, rates were 2 percent in Maui and Hawaii County and 8 percent of Kauai’s samples were unhealthy.

The report singled out three Kauai’s beaches as having the dirtiest beachwater in the state including Lumahai Beach (29 percent), Kalihiwai Bay (27 percent ) and Waimea Recreation Pier State Park (24 percent).

Other states with low rates of contamination included: New Hampshire (1 percent), New Jersey (2 percent) Oregon (3 percent) and Delaware (3 percent). Highest offender states included:  Louisiana, (37 percent), Ohio (21 percent) and Indiana (16 percent).

The report said about 8 percent of beachwater samples nationwide exceeded public health standards in 2010. Pollution from stormwater runoff and sewage overflows last year contributed to the second-highest number of closing and advisory days in more than two decades, the council said.

Most bacterial contamination occurs during winter, when heavy rains overload storm drains and sewage systems, washing waste into the sea. 

Swimming in such pollution can cause gastrointestinal, respiratory and other illnesses and is of particular risk for children and the elderly whose immune systems may not be as strong. The Environmental Protection Agency estimates that up to 3.5 million people become ill from contact with raw sewage from overflows every year.

Swimmers are advised not to swim near storm drains or go into the waters within 72 hours of a rain when pollution levels are typically higher.

The Associated Press contributed to this story.