A large sewage spill from the West Point Treatment Plant near Discovery Park in Seattle has prompted a ban on shellfish harvesting along the eastern shoreline of Bainbridge Island, the Kitsap Public Health District announced Thursday.

Two other sewer overflows reported by the city of Bremerton have also spurred the expansion of the existing no-contact advisory for the Port Washington Narrows and Sinclair Inlet through Thursday, Feb. 16. The ban now also includes Dyes Inlet.

According to the Bremerton city officials, two sewer overflows have been found near the north and south shores of the Port Washington Narrows, and an estimated 33,000 gallons has been spilled.

Health officials said both spills were caused by heavy rainfall. The overflows of sewage occurred between 8 and 9 a.m. Thursday.

Officials said combined sewer overflows — also called CSOs — are a diluted mixture of untreated sewage and stormwater that have spilled into Puget Sound.

The CSOs occur after stormwater flows enter the sanitary sewer system during heavy rainstorms. Under these conditions the system functioned as designed, officials said, discharging excess flow into marine water to prevent the back up of sewage into individual homes and businesses.

On Bainbridge, the health district, in cooperation with the Washington State Department of Health, has issued a no-contact advisory and shellfish harvesting ban for the eastern shoreline of the island, as well as the shoreline between Jefferson Point and Restoration Point, including Port Madison Bay.

Additional signage is being posted to warn the public in affected areas.

During a no-contact advisory, the public is warned to avoid contact with the water in the affected area.

People should also avoid direct skin contact if possible, and immediately wash with soap and water if they have exposure to the water.

King County officials said the spill at the West Point Treatment Plant happened early Thursday morning because of an equipment failure that occurred at about 2 a.m. during heavy rainfall and high tides.

The facility is operating in “emergency bypass mode” to protect the sewage treatment plant from flooding that could severely damage equipment.

Untreated wastewater is being pumped into Puget Sound via an outfall pipe that is about three-quarters of a mile offshore and 240 feet deep in Puget Sound.