The construction and opening in April 1994 of the 200 metre wide Dawesville Channel in April 1994 connecting the Peel-Harvey estuary at Mandurah in Western Australia, to the Indian Ocean, has had an impact on the integrated phytoplankton composition and density of the eutrophic waterwayPeel-Harvey Estuary. The Channel. connects the Harvey Estuary at Mandurah in Western Australia, to the Indian Ocean. The almost annual spring-summer blooms (max. ca. 600,000 cells per mL) of the hepatotoxic cyanobacterium Nodularia spumigena Mertens that occurred in the eutrophic estuary between 1978 and 1992, have ceased to occur since the channel Channel was opened to the sea. Though the estuary Estuary still experiences occasional phytoplankton blooms these are dominated mainly by estuarine and marine species of diatoms. There have been rare isolations of Nodularia in the estuary Estuary and these have been attributed to material brought in from estuarine reaches of the Serpentine River portions of rivers. Annual blooms of Nodularia still continue to occur in the Serpentine River estuary this river.