The Vasse-Wonnerup Estuary is a shallow, nutrient-enriched estuarine system located behind Busselton, intermittently open to Geographe Bay in the Indian Ocean. This bird-rich environment is a significant conservation area, though its catchment has been substantially modified through historical land clearing and flow diversion. The system comprises saline flats, swampy depressions, and low-lying terraces, creating a mosaic of habitats. It is a low-inflow estuary known for its productive but sometimes fragile water quality, with management focused on mitigating risks like algal blooms and fish deaths.