During June, July and August, blooms of blue-green algae at the Indian Head water quality monitoring station south of Washington D.C. on the Potomac River had an average density of 10,239 cells/ml (Figure 1). One of the three primary blue-green algal species being monitored, Microcystis aeruginosa, had concentrations of 3528 cells/ml for the summer (Figure 1). These concentrations were only the 9^th highest summer means for total blue-green cells and Microcystis in the last 17 years.

Figure 1. Historical time series (1985-2001) for summer mean 
concentration (cells/ml) of Total Blue-green algae and only 
Microcystis aeruginosa at Potomac River, Indianhead Station.  
(Summer = June, July and August)