Broke Inlet, originally named Broke's Inlet, is an inlet in the South West region of Western Australia located 19 km west of Walpole. The inlet is a large shallow estuary at the eastern end of the d'Entrecasteaux National Park, linked to the Southern Ocean by a narrow seasonally open channel situated between two high sand dune systems. The inlet is the only large estuary left in the South West that has not been significantly altered by development within its catchment area or along its shores. The catchment of the inlet has an area of 928 km2 and the inlet itself has a surface area of 4800 ha with a total volume of 72000000 m3. The inlet receives an annual inflow of 187000000 m3, mostly from the Shannon River and discharges 157000000 m3 annually. The water in the inlet is brackish and generally has half the salinity of sea water. The salinity varies greatly depending on river discharge, the season and whether the bar is open or not. Broke Inlet is listed as a regionally significant wetland with Environment Australia. The inlet's and locality's names are thought to be based on Philip Broke, captain of HMS Shannon (1806), a frigate of the Royal Navy, best known for its victory over USS Chesapeake (1799) in 1813. Shannon is the name of both a river and a neighbouring locality. Both names were first recorded on a map in 1833.