State officials today said they are investigating the circumstances that led to significant coral damage near the entrance channel to Honolulu Harbor after dredging work done by a contractor.

The state said U.S. Army Corps of Engineers hired Healy Tibbitts Builders Inc. for dredging work at the harbor.

Healy Tibbitts allegedly dragged the dredging platform’s anchor and cable across several coral colonies — toppling one estimated to be several hundred years old — and deposited debris on top of them, according to the state Department of Land and Natural Resources.

“This is a large and significant damage event,” said state Division of Aquatic Resources Administrator Brian Neilson in a news release. “The last few days our dive teams have been in the water doing further assessments and documenting the scope of the damage.”

Divers from the U.S. Fish and Wildlife Service who were conducting water quality monitoring first noticed the damage last Tuesday and reported it to state officials.

They observed and photographed damage stretching across an estimated 17,500 square yards that included both broken and toppled colonies, as well as coral smothered by dredged material.

Among the corals damaged is a significantly large Porites evermanni colony estimated to be several hundred years old, according to experts.

Divers found this previously healthy colony of live coral overturned, on the bottom, and in danger of dying due to suffocation, offiials said. Saving this colony will require specialized equipment to return it to an upright position as soon as possible to increase its chances of survival.

On Friday, state divers will attempt to reattach broken corals using a special marine epoxy, and collect other fragments for the Anuenue Coral Restoration Nursery on Sand Island, where specialists hope to grow them out for eventual return to the ocean.

“We’re already seeing mortality among some of the corals that were damaged,” said David Gulko, manager of the coral restoration nursery. “Time is of the essence, with the summer’s first south swells imminent, so we need to fix as much damage as we can, quickly.”

The documented damage may be presented to the Board of Land and Natural Resources, which has the authority to impose fines on responsible parties to pay for resources damages and remediation efforts.

“Healy Tibbitts understands the significance of Hawaii’s precious natural resources, and we are committed to doing everything we can to take immediate restorative action and mitigate further damage to the coral reef,” said Emmett Kinney, Vice President of Healy Tibbitts Builders Inc. in a statement. “To that end, we have retained help from Marine Research Consultants, Inc. and Sea Engineering, Inc. to rapidly commence mitigation and restoration efforts.”

This is one of the most significant incidents of damage done to Hawaii reefs since 2009, according to DLNR, when the USS Port Royal, a U.S. Navy missile cruiser, ran aground and damaged the coral reef within sight of Honolulu International Airport.

The Navy agreed to pay $8.5 million to the state for that incident, DLNR said, the largest settlement for reef damage at that time. As part of remediation efforts, divers collected and reattached 5,400 loose coral colonies.