Leschenault Estuary, known to the Noongar people as Derbal Eelap, is a 25 km lagoon lying just north of Bunbury, separated from the Indian Ocean by a long sand dune peninsula. The estuary covers 25 square kilometres and functions as a major fish nursery and waterbird habitat, supporting up to 62 species of waterbird in its tidal salt marshes.
The most interesting feature for visitors is the ancient mangrove colony at the estuary's southern end. These white mangroves — the southernmost in Western Australia — are thought to be around 2,500 years old, and a boardwalk with explanatory signage winds through them at water level. The estuary is part of Kalgulup Regional Park, which offers flat cycling and walking tracks along the waterfront.
Early morning and late afternoon are the best times for birdwatching. Black swans, pelicans, cormorants, and various species of egret are common; wading birds concentrate on the exposed mudflats at low tide.