One of Hawaii’s largest freshwater marshes, Kawai Nui provides flood protection for the town and a habitat for endangered waterbirds, and is also one of the largest remaining fishponds once used by ancient Hawaiians. You may see rare birds, including the koloa maoli (Hawaiian duck), aeʻo (Hawaiian black-necked stilt), ʻalae kea (Hawaiian coot) and kolea (Pacific golden plover). Several local groups work to preserve and restore the marsh.

　　To access the area, park in the lot at the end of Kaha St, off Oneawa St, just over a mile northwest of Kailua Rd. It's a very historical spot: for over a thousand years it was a fishpond fed by copious amounts of freshwater. In the 1800s it was partly filled to allow the farming of taro and rice.