Lyngbya majuscula is a filamentous blue-green alga with worldwide distribution throughout tropical and subtropical regions. Since the first reports in the late 1950\'s in Hawaii and later in Okinawa, swimmers coming into contact with this cyanobacterium have contracted acute dermatitis. Strong anecdotal evidence suggests similar episodes around Fraser Island and other locations along the Queensland coast among recreational water users as well as commercial fishers. Of the over forty unique biologically active chemicals isolated from this species, three toxins, debromoaplysiatoxin, aplysiatoxin and lyngbyatoxin A have been found to be the major cause of dermatitis. These three toxins are all tumor promoters, binding to phorbol esters receptors leading to the activation of protein kinase C. Examination of the toxins present in the Australian blooms, and their biological activities will be made, as well as comparisons to other blooms of this species worldwide. A prospective cohort epidemiological study over three years will gather information on the location and type of water activity to assess the effect of algal blooms and toxin production on the health status of water users. It is envisaged that cohorts of volunteers, both recreational water users and commercial fishers, will be recruited at beach and other locations. Participants in the study will be asked to fill out a short questionnaire on location. Two to seven days later a follow-up telephone call will be placed and further questions on changes in health status 48 hours after water exposure asked. Assessment of change in health status will allow the first measurement of the number of people effected by this organism in Australia and estimates of the severity, spatial and temporal distribution of dangers and effects of length of time and use of clothing during water exposure. Correlation will be made with size of bloom, amount and type of toxins present and other environmental factors. Preliminary data will be presented at the conference.