The city of Houston has been devastated by a flood of biblical proportions days after Hurricane Harvey roared ashore, but another grave threat is looming. Health officials in the state of Texas are warning about an increased risk of illnesses and hazards because of the floodwaters, and concerns about mosquito-borne illnesses, viral infections, and even carbon monoxide poisoning are rising.

The number one concern for officials is chemicals. Floodwaters can be contaminated with all sorts of nastiness, like chemicals that were sitting in people’s garages or toolsheds. As a result, officials are advising people to immediately shower and wash their hands if they come into contact with the floodwaters.

The government is advising people to toss medications or foods that touch floodwater, as even foods wrapped in plastic packaging can become dangerous due to the floods thanks to bacteria that lurk in the dirty water.

The problems could linger for weeks or even months, and it could make many places totally uninhabitable.

“If you are in a small enclosed area in an alternate care facility and you have really bad diarrhea, it’s going to be hard in these situations to practice proper infection control,” Dr. Amesh Adalja, a senior associate at the Johns Hopkins Center for Health Security, told Reuters.