The state Department of Land and Natural Resources Wednesday will announce the purchase of Kailua’s 67.18-acre Hamakua Hillside, in an ongoing effort to preserve the adjacent Hamakua Marsh.

The state purchase culminates a four-year effort to protect the hillside and the marsh in their natural state.

The marsh, the largest remaining natural wetland in Hawaii, is home to all four endangered endemic Hawaiian water birds, the Hawaiian duck, Hawaiian moorhen, Hawaiian coot and Hawaiian stilt.

Kaneohe Ranch Co., which sold the land to the state, promised in 2003, not to develop the land in order to protect the marsh.

In 1994, the Harold K.L. Castle family donated Hamakua Marsh to Ducks Unlimited, a private environmental protection organization, with the understanding that the group would improve and restore the marsh and then donate it to the state so it could be protected in perpetuity.