Australian fisheries biologists suspect there is a link between runoff from acid sulphate soils and red spot disease or epizootic ulcerative syndrome (EUS), an ulcerative skin disease of estuarine fish. Researchers have shown that the primary cause of mortality in affected fish is the invasion of skin and underlying muscle by an aquatic fungus, Aphanomyces. It appears that changes in estuary water quality (including high acidity) may damage the skin of fish exposed to these changes.