The Charles County Health Department has extended indefinitely its warning to avoid contact with streams in a 15-square-mile area between White Plains and La Plata.

County Health Officer Chinnadurai Devadason said isolated water testing results indicate the continued presence of elevated levels of enterococcus bacteria, which may cause illness.

Officials have not identified a specific cause for the contamination, which has been present since the beginning of the summer. Sewage overflows from the La Plata Wastewater Treatment Plant are the likely source of most of the bacteria, according to the Health Department, but until a full investigation is conducted, it is not known what other factors could be affecting the streams.

Because testing of water samples from the streams will not be done again until the spring, the advisory is unlikely to be lifted until that time. "If we get a lot of rainfall, there may be some dilution of the streams. Otherwise, the flow of water is limited, and the conditions are unlikely to change," Devadason said.

The area under the advisory is bounded on the north by Route 227 in Pomfret, continuing east to Route 301 at Willetts Crossing, south to Route 6 in La Plata and then west along Route 6 to Hoghole Run. Water samples were taken in Hoghole Run, Port Tobacco Creek, Jennie Run, Wills Branch and feeder streams in those areas.