U.S. Army Corps of Engineers, Fort Worth District, Environmental Planner Billy Colbert listens intently as Dr. Gary O. Dick, Director of the Engineer Research and Development Center's Lewisville Aquatic Ecosystem Research Facility at Lewisville Lake explains current testing results at the fish ponds. The ponds are being analyzed to see what density of fish will be necessary to control an infestation of non-native hydrilla in a watershed.