(CNN)Before you head to the beach this summer, you might want to double-check the water conditions.
Last year, nearly 60% of 4,523 beaches tested across the United States demonstrated unsafe water pollution levels on at least one day, according to a report released Tuesday by the nonprofits Environment America Research & Policy Center and Frontier Group.
These 2,585 beaches had bacteria levels that exceeded the US Environmental Protection Agency's "Beach Action Value" threshold, which it recommends states use to provide an early alert to beachgoers who may be particularly sensitive to contaminants.
On the higher end of the scale in the new report, Inner Cabrillo Beach in Los Angeles County had 85 potentially unsafe days out of 175 days sampled. By contrast, Bethany Beach in Delaware's Sussex County tested potentially unsafe on one of 33 sampled days.
The report compiled data from sampling conducted by local, state and federal agencies submitted to the National Water Quality Monitoring Council's Water Quality Portal.
It warned that sewage and fecal contamination of swimming areas pose a public health threat. Humans who come into contact with it can develop gastrointestinal illness, respiratory disease, infections and skin rashes, the report said.