Northern snakehead (NSH) (Channa argus), recently established a population in the Potomac River catchment. This large, piscivorous, air-breathing fish may pose substantial risk to native fishes. To understand habitat preferences, home range, and dispersal patterns of NSH in this novel environment, we implanted 49 fish (weighing 790-3489 g; mean = 2065 g) with radio transmitters in October 2006. Fish were captured and released in three tributary embayments in Virginia. We will locate each fish monthly through March 2007, and eight times per month during April-November 2007. The geo-referenced locations of fish will be recorded, with measures of water quality (temperature, turbidity, salinity, dissolved oxygen) and habitat (depth, cover, substrate). Identical measures will be taken at random locations paired with fish locations, enabling us to characterize habitat selection. Through winter 2007, most fish were found in shallow (<1.5 m) offshore milfoil beds in the bays where they were released. A few fish were observed in the mainstem Potomac in similar habitat, and one moved >5 km upstream. However, the deep, flowing waters of the mainstem appear to be a barrier to migration; no tagged fish crossed the mainstem or left the study area. Eight fish in Dogue Creek were located every 1.5 hours for 12 hours on October 31. Most fish moved little during the day, and more frequent and longer movements (up to 1 km) were observed after sundown. Initial results suggest a strong preference for macrophyte cover, and a restricted home range with occasional long distance dispersal.