The U.S. Environmental Protection Agency has ordered the state Health Department to post signs at Gillin’s Beach on Kauai to alert the public of high bacteria levels.

The EPA raised concerns about the water in a letter sent to the state July 25, asking that signs be posted and for the Health Department to further investigate the source of Enterococcus bacteria, which indicates fecal contamination. The state has determined the source is not human fecal matter.

The federal agency indicated water quality at the mouth of Waiopili Stream, near the Makauwahi Cave Reserve, exceeds Hawaii’s acceptable water quality standards. The letter was based on the agency’s review of the Health Department’s sanitary survey from testing of the Mahaulepu Watershed-Waiopili Ditch from November 2014 to March 2015.

As a recipient of a Beach Act grant, the state receives $300,000 in annual funding from the EPA and is required to post signs at beaches when the level of Enterococcus is above 130 units per 100 milliliters. Water samples taken in April at Gillin’s Beach were recorded at 478 units per 100 milliliters, the EPA said.

Although standards for Enterococcus are based on state and national guidelines, Deputy Director Keith Kawaoka of the state’s Environmental Health Administration said Hawaii is unique compared with other states due to its tropical weather, animals and vegetation that contribute to bacteria levels.

“We’re trying to work out a reasonable path forward,” Kawaoka said. “We do recognize the need to inform the public of potential hazards not only in that area, but across the state.”

Nancy Woo, assistant director of the EPA’s Ecosystems Branch, Water Division, said in the letter that regardless of the source, “elevated enterococcus levels can pose a potential public health risk to people who recreate in the impacted water.”

In addition to signs, the federal agency strongly advised the Health Department to implement protection measures such as limiting access to the site and conducting outreach to inform the public.

Two years ago the Surfrider Foundation Kauai Chapter and Friends of Mahaulepu complained to the Health Department and EPA about elevated bacteria levels in the stream. Opponents of a proposal to build a dairy at Mahaulepu fear its operation would exacerbate bacteria levels.

The Health Department’s survey indicated “there is no significant impact to the Waiopili Ditch from any activity that can be attributed to the proposed dairy.”

Carl Berg, chairman of the executive committee of the Surfrider Foundation Kauai Chapter, said, “The Surfrider Foundation is very pleased that the EPA did a critical review of the sanitary survey and pointed out all of the shortcomings.” The letter “validates our concerns,” said Berg, who also heads the Blue Water Task Force, which measures water quality in ocean and streams.

The survey noted the risk of illness from exposure to water affected by animal waste is significantly lower than the risk of water affected by human sewage. Nevertheless, Berg said, elevated bacterial levels tied to animal fecal matter can be a public health concern.