The state Department of Health is advising the public to stay out of Kaha­luu Lagoon and the channel leading to Kane­ohe Bay after tests revealed unusually high levels of harmful bacteria in the water.

Caution signs have been posted at the affected areas as the Health Department investigates the source of the contamination and determines the appropriate follow-up steps.

The tests were conducted by the department’s Clean Water Branch in response to a request from the Kaha­luu Neighborhood Board that cited infections and illnesses suffered by canoe paddlers, boaters and fishermen after entering the recreational waters. Initial readings found high levels of enterococcus and clostridium bacteria, which could indicate the presence of untreated sewage.

In a statement released Friday, deputy director of environmental health Gary Gill said the contamination may be due to a large concentration of residential cesspools in the area.

"This untreated sewage contains pathogens that can spread disease, as well as nutrients that can degrade water quality and harm coral reefs," Gill said. "With this potential source of contamination, the department will conduct further studies to determine the extent of the problem and what can be done to protect people and the environment."

The DOH has made available a set of documents that provide additional information on the affected areas, bacteria readings and the DOH response, which can be accessed at goo.gl/xAhpls.