SAN DIEGO -- Various Mission Bay recreation areas were closed to the public Wednesday due to an influx of pollution possibly caused by illegal sewage dumping, authorities reported.

Routine water-quality monitoring in the man-made harbor northwest of downtown San Diego detected the contamination Tuesday, according to the county Department of Environmental Health.

Precisely where the pollution -- believed to be solid sewage debris -- came from was unknown, but the suspected source was an unlawful discharge from a sanitation system, officials said.

The DEH posted signs warning of bacterial health hazards along swimming beaches at De Anza Cove, north Crown Point and Campland on the Bay, and in recreation areas between Vacation Isle and the harbor's eastern boat dock.

The warnings will remain in effect until follow-up testing deems the sites safe again for human contact.