Fresh water skin disease (FWSD) is a disease of marine cetaceans in coastal and estuarine environments, caused when they are exposed for extended periods to water with lower than normal levels of salt (hypo-saline). It has been observed in dolphins that were displaced into freshwater lakes, and in normally-salty lakes and estuaries where salinity has dropped suddenly due to flooding or storm runoff. The histology and pathology from dolphins that died in the 2007 and 2009 Australian events was published in 2020, with the name "fresh water skin disease".