Thompson Creek is a coastal estuary system flowing through rural and coastal areas of the Surf Coast Shire before entering Bass Strait near Breamlea. It is a significant waterway within the Otway Basin, with its estuary dynamics playing a crucial role in the surrounding Karaaf Wetlands. The system's condition has been assessed as poor in most reaches, with elevated phosphorus levels. The estuary mouth's opening, whether natural, managed, or illegal, is a critical event that dramatically affects water levels, salinity, and fish habitat, with closures sometimes maintained to provide environmental benefits despite causing localized flooding.