Several coastal areas in southeast Queensland, Australia have been affected by blooms of the cyanobacterium Lyngbya majuscula Gomont (Mermaid hair). Lyngbya majuscula blooms have caused respiratory irritation, eye inflammation and severe contact dermatitis in fisherman and swimmers as well as causing reduced fish catch, seagrass loss and localized inputs of nitrogen through nitrogen fixation. Lyngbya majuscula collected in the summers of 1996-7 and 1997-8 had cells 10 μm long and 30-40 μm wide, forming filaments up to 30-40 cm long. Lyngbya majuscula distributions that have been linked to reports of dermatitis were identified at 3 sites along a 240 km stretch of coastline: Deception Bay (northern Moreton Bay), Rainbow Beach (south of Fraser Island), and Waddy Point (northern Fraser Island). Previous seasonal blooms of increasing severity have been reported by fishermen and swimmers over the past several years. The cause(s) of these blooms is being investigated, in particular the possibility that increased availability of iron derived from exposure and aeration of hydric soils stimulates cyanobacterial growth.