The Coast Guard cutter Morgenthau, berthed at Coast Guard Base Sand Island, improperly discharged about 4,600 gallons of wastewater and sewage into Honolulu Harbor, the Coast Guard confirmed Tuesday.

The spill was touched off by a misalignment of the overboard discharge valve, which was locked in accordance with procedures for entering port, but incorrectly in the open position, according to a news release issued by the Coast Guard.

The state Department of Health’s Clean Water Branch reported the spill Monday night after being notified by the Coast Guard that it had discharged at the Sand Island base from the open valve.

Signs warning people to stay out of the water on the Diamond Head end of Sand Island State Park were posted Tuesday.

In the release, the Coast Guard said the valve may have been left open at 6:30 p.m. Friday when the vessel docked at Sand Island. It was closed about 9:30 a.m. Monday when a ship’s engineering officer noticed the discharge into the harbor.

The ship’s sewage system, which is set to pump when the holding tank reaches about 1,250 gallons, had automatically discharged four times during that period. The contents of the tank include wastewater from the sinks and showers and sewage, the Coast Guard statement said.

The Health Department estimated that 4,600 gallons of wastewater was discharged into the harbor.

The Coast Guard said a Morgenthau crew member reported the odor of sewage at 9:30 a.m. Monday. A ship’s officer then went to the side of the ship and saw brown water flowing overboard through the sewage discharge port, which is intended for use only at sea, and immediately secured the system.

"As one of our missions is to protect the environment, I take this very seriously," Capt. Richard Mourey, commanding officer of cutter Morgenthau, said in the release. "We will take the necessary steps to ensure this does not happen again."