Pathogens were not seriously considered as biological control agents for aquatic plants in the United States until the Chesapeake Bay Eurasian watermilfoil decline occurred in the 1960s. The decline and suggestion that it was induced by pathogens spawned interest in the use of pathogens as biological control agents for nuisance aquatic species. In the years that followed, emphasis was placed on finding pathogen agents for some of the most problematic aquatic weeds, including waterhyacinth, Eurasian watermilfoil, and hydrilla. The scientist that has contributed the most to our knowledge of pathogen biological control in aquatic plants has been Dr. Raghavan Charudattan (University of Florida, Gainesville, FL). For the past 40 yr, he has authored or coauthored more than 50 manuscripts devoted to the subject in peer-reviewed journals, books, and proceedings.

The aim of this study was to evaluate the effect of the macrophyte waterhyacinth on the water quality of a reservoir in Colombia. Postinvasion water quality assessments were performed during three different hydrological periods and compared with preinvasion data. The results show that water quality has improved, especially in terms of transparency, showing an increase in Secchi disk values from 0.3 to 2 m (1 to 6.6 ft). The analysis strongly suggests that the improvement in water quality is due to the filtering and precipitation effects provided by waterhyacinth. This case highlights the dilemma of managing an invasive species that provides a beneficial ecological service while posing a high ecological risk.