The blue-green algal bloom in the Hawkesbury River at the Sackville Ferry during the summer of 1991/2.

The Haswkesbury-Nepean River is an important resource for the Sydney Basin. The river is used extensively for recreation, irrigation, water supply and effluent disposal. Since European settlement, human activity in the catchment has caused a rapid deterioration in water quality and it is now unsatisfactory for many uses (SPCC,1983). IN particular, the incidence of blue-green algal (cyanobacteria) blooms has increased in recent years as a consequence of eutrophication (Heath & Cannon, 1990). The presence of algal blooms at the North Richmond abstraction of the off-take have caused taste and odour problems in the past. The presence of toxins was demonstrated in blue-green algal blooms at this site in 1983, 1985 and 1988, and this is a cause for concern (water Board, unpublished data).