A corroded, faulty pipe used to pump molasses onto Matson, Inc. cargo ships at Sand Island spilled an estimated 233,000 gallons of the dark and syrupy substance into Honolulu Harbor on Monday, killing hundreds of fish there, company and public health officials say.

The state’s Department of Health is concerned about a large plume that’s still in the harbor today — indicating the total molasses spilled was “significant,” Department of Health spokeswoman Janice Okubo said.

“There is a huge plume in the water at Honolulu Harbor,” she said.  It appears to be depleting oxygen from the water, causing fish to beach themselves, health officials say. 

A private contractor is removing the dead fish, in part to help keep predatory fish — including sharks — away from the area, Okubo said. State health officials are also posting signs around the area warning people not to swim there.

However, there’s no cleanup planned because health officials haven’t determined a way to remove the substance from the water — the molasses will likely have to dissipate and dissolve on its own, Kubo said.

Matson, which ships molasses exports from Hawaii to the mainland US, self-reported the spill Monday to the state DOH’s Hazard Evaluation and Emergency Response office on Monday after workers started seeing a brown substance in the water and smelled something unusual, company spokesman Jeff Hull said.  

The shipping company then hired divers with Pacific Environmental Company, who inspected Matson’s loading operation underwater and discovered the faulty pipe as the cause, according to a statement Matson released today.

The company is “fairly certain” the leak did not occur in the molasses tanks or the ship, and the pipe they’ve identified as the source was not normally used to pump the substance onto Matson ships, Hull added.

There’s no molasses being pumped onto Matson ships at this time, and the company is working with DOH and other state agencies, including the Department of Land and Natural Resources and the Department of Transportation (which regulates the harbors) to address the spill, Hull said.

“Matson regrets that the incident impacted many harbor users, as well as wildlife,” Matson’s statement read. “We take our role as an environmental steward very seriously and … we are taking steps to ensure this situation does not happen again.”

The last reported molasses spill in Hawaii occurred in December 2003, when a two-inch hole in a state transmission line spilled 50,000 gallons into Maui’s Kahului Harbor. In that case, the molasses, from Hawaiian Commercial & Sugar Co., was supposed to be pumped aboard a Matson barge. The spill was reported when officials noticed a discrepancy between the amount of molasses leaving its storage tank and that received by the barge.