Three North American and 1 European viral hemorrhagic septicemia virus (VHSV) isolates taken from either a marine, freshwater, or estuarine host were assessed for survivability in raw and filtered freshwater and seawater at temperatures ranging from 4 to 30 degrees C. All 4 isolates were substantially more stable in freshwater than in seawater, and higher survival was observed at lower water temperatures. The average time required for 99.9% inactivation of VHSV in raw freshwater at 15 degrees C was 13 d, while in raw seawater VHSV was inactivated within an average of 4 d. No consistent correlation was observed between the origin and the stability of the virus isolates. Freshwater isolates were not always the most stable in freshwater; similarly, seawater isolates were not consistently more stable in seawater. Virus survival was greatly enhanced in filtered freshwater with some virus strains remaining infective after 1 yr at 4 degrees C.