The brown floodwaters left by Hurricane Harvey contain some very nasty health dangers, experts warn. Microbiologist Dr. Terry Gentry told Good Morning America that the water contains 125 times more bacteria than what is considered safe for swimming. He tested the water and found high levels of E. coli and coliform, bacteria associated with human and animal waste. The moving water picked up everything in its path, including fertilizer, toxic chemicals and raw sewage from flooded systems.