King Sound, encompassing Stokes Bay and the tide-dominated delta of the Fitzroy River, is a globally singular system. Most of the Sound remains a wilderness set in a monsoonal, semi-arid climate. This large water body is fringed by broad tidal mudflats with low energy seas dominated by an extreme tidal regime.
King Sound functions as a seasonal estuary and is the receiving basin for the Fitzroy, May and Meda Rivers (MPRSWG, 1994). The Fitzroy River delta has the largest tidal range of any tide-dominated delta in the World (Semeniuk and Brocx, 2011). Freshwater in the fractured bedrock discharges into the tidal zones of the region inthe wet season and continues into the dry season. This is a globally significant process, controlling the occurrence and maintenance of mangroves in the high tidal zone (Cresswell and Semenuik, 2011).The tidal mudflats and mangroves provide nursery habitat for a wide variety of fish (Loneragan et al.,2002) and crustaceans, which are important prey for inshore dolphins. Australian snubfin dolphins (Orcaella heinsohni) and the Indo-Pacific humpback dolphin (Sousa chinensis) use the tidal rivers, while bottlenose dolphins (Tursiops spp.) are found out in the embayment (Thiele, 2008).King Sound and the adjacent Fitzroy River are the only known nursery areas for freshwater sawfish (Pristis microdon) in the Kimberley and are a significant stronghold for this and other sawfish species worldwide (Thorborn and Morgan, 2005a, 2005b). The Fitzroy features four of the world’s most endangered fish: the freshwater sawfish (P. microdon), the dwarf sawfish (Pristis clavata) and the northern river shark (Glyphis garricki), all of which are listed as critically endangered by the IUCN. The fourth species, the freshwater whipray (Himantura chaophraya), is IUCN-listed as vulnerable (Morgan et al., 2004; Thorburn et al., 2004; Thorburn and Morgan, 2005a, 2005b; IUCN, 2011).These may be some of the world’s only remaining viable populations of some of these species (Morgan et al., 2011).The organic mound-springs complex known as Big Springs, on the eastern shore of King Sound, provides a significant area of habitat and refuge. The complex includes dense wet rainforest species, dominated by forests (20 metres tall in some places) of Terminalia macrocarpa , a species not otherwise known south of Walcott Inlet. Big Springs is a rare feature in this region and the best example of seepage rainforest in the Dampierland bioregion (May and McKenzie, 2002). It is listed on the National Directory of Important Wetlands.
Mangroves are very well developed in the Kimberley and noted internationally for their relatively pristine condition (IUCN, 1981). Unlike elsewhere in the world, they have not been subject to broad-scale deforestation or fragmentation through coastal development and are noted for being a rare system of mangroves set in a tropical, largely macrotidal environment (Cresswell and Semenuik, 2011). King Sound alone supports 13 mangrove species (Semeniuk, 1980); the mangrove habitats of King Sound are extensive, healthy, diverse and largely intact.