Storm surge associated with Hurricane Katrina and the breach of levees protecting New Orleans, Louisiana allowed floodwaters from Lake Pontchartrain to inundate 80% of the city. Environmental samples were collected during September 16-18, 2005 to determine immediate human and wildlife health hazards from pathogens and toxicants in the floodwaters. Baseline information on potential long-term environmental damage resulting from contaminants in water and sediments pumped into Lake Pontchartrain was also collected. Concentrations of aldrin, arsenic, lead, and seven semivolatile organic compounds in sediments/soils exceeded one or more United States Environmental Protection Agency (USEPA) thresholds for human health soil screening levels and high priority bright line screening levels. High numbers of Aeromonas spp., pathogenic Vibrio spp., and other coliform bacteria were found in floodwater samples. Alligator and snake tissues did not contain excessive toxicant concentrations. Initial findings suggest numerous environmental contaminants are present in New Orleans and support the need for further evaluation of the extent of those threats.