The euryhaline hydroid, Cordylophora caspia, causes fouling problems in Europe and the United States. Researchers propose that this hydroid is becoming more prevalent in freshwater habitats as evidenced in Morris, IL where it was found clogging intake pipes and screens at a power plant, Midwest Generation's Collins Station. Our objective was to determine ways to curtail growth or kill C. caspia. Hydroid colonies in the laboratory were exposed to thermal treatments of 35, 36.1, 37.7, and 40.5 degrees C ranging from 1 to 8h. Hydroids did not survive at the two highest temperatures. Colonies exposed to lower temperatures exhibited varying degrees of survival relative to temperature and exposure time and demonstrated regeneration. In addition, experiments using chlorine were conducted using concentrations ranging from 0.2 to 5.0 mgl(-1). Chlorine experiments using exposure times of 105 min and three 20 min exposures in a 24h period did not kill colonies but were effective in curtailing growth. Thermal treatments are preferred because they are effective and result in less environmental impact in receiving waters than chemicals.