The longtime effort to restore wetlands at Hamakua in Windward Oahu has reached a major milestone: acquisition of a hillside that recharges the nearby marsh, helping to preserve wildlife and native plants.

State officials held a ceremony Wednesday in Kailua to announce the purchase of 67 acres of Hamakua hillside from Kaneohe Ranch, including drainage gullies emptying into the marsh.

The Hamakua hillside and marsh and nearby Kawainui Marsh make up the largest natural wetlands in the state.

State Land Board Chairman William Aila said the acquisition caps off more than 15 years of work by the state and a variety of groups to restore the marsh lands, home to several endangered Hawaiian bird species.

“It took a lot of blood, sweat and tears,” Aila said. “Hamakua is an important and unique place for wetland and watershed protection.”

The purchase means there will be no housing built on the makai slope, reducing the chances of pollution contaminating the marsh, he said.

Aila praised the Harold L. Castle Foundation and its real estate arm Kaneohe Ranch Management Ltd. for enabling the state to buy the hillside for $1.17 million. The state contributed $450,000, and the U.S. Fish and Wildlife Service’s Recovery Land Acquisition Program, $720,000.

Along Hamakua Drive mauka of Kailua Town, the marsh is the habitat for the endangered Hawaiian duck, moorhen, coot and stilt.

State forestry official David G. Smith, standing near a Hawaiian coot and duck swimming in Hamakua Stream, said 25 years ago the Hamakua marsh was full of alien mangrove trees.

“It was completely overgrown. You couldn’t see the stream from here,” said Smith, now the forestry manager on Oahu.

In 1994, the Castle family donated 22.7 acres of marsh to the environmental group Ducks Unlimited to improve and restore the wetlands.

Ducks Unlimited dedicated the marsh to the state in 1995, after the restoration and the removal of some of the mangrove trees.

The state later cleared out the remaining mangrove.

Kaneohe Ranch manager Mitch D’Olier said the Castle family kept its pledge to preserve the hillside.

“Now, this environmental treasure will be protected in perpetuity,” D’Olier said.

D’Olier praised former Kaneohe Ranch manager Randy Moore and wildlife museum curator Andy Engilis Jr. for their early work to restore the marsh.

Smith said the state has planted native milo and kou along the hillside.

“What we’d like to do is reforest the hillside with native trees,” he said.