When Hurricane Harvey pounded Houston, Texas, this week, it submerged the surrounding area under several feet of floodwater and left sections of the country’s fourth-largest city uninhabitable. The hurricane did more than structural damage; powerful storms come with health risks, from mold to contamination, and experts worry some of these problems will linger long after the waters recede.

Drowning

Drowning is the most common health risk associated with hurricanes. The World Health Organization reports that as many as three-quarters of all deaths during a flood are attributed to drowning, and a recent Buzzfeed article reported that the majority of people who have died in Hurricane Harvey drowned.

Drowning isn’t the only danger from floodwaters brought on by such natural disasters. These murky waters also hide dangerous objects, such as broken glass and sharp metal edges, that can cause significant harm to those who wade in them, the Centers for Disease Control and Prevention warns.

Bacterial Infections

Floods are also comprised of sewage overflow, and debris and garbage picked up along the way, which makes them a cesspool of bacteria that can lead to a number of infections, some of which are life threatening.

“What’s going to happen is that drinking water and wastewater treatment facilities have been overwhelmed, and sewage systems have been overwhelmed as well,” Michelle Fanucchi, Ph.D., associate professor of Environmental Health Sciences at The University of Alabama at Birmingham, told Medical Daily. “There will be raw sewage in the flood water, containing high levels of E.coli, hepatitis, and things like that.”

According to Newsweek, gastrointestinal bacterial infections, such as Escherichia coli (E.coli) and Shigella, are particularly common following a flood. Other less common bacterial infections, such as Vibrio illness or Legionnaire’s disease, can also spike following a natural disaster.

“In addition to raw sewage that’s out there, the flood waters also contain all sort of chemicals, such as gasoline and water, and anything like that,” Fanucchi told Medical Daily, explaining that prolonged skin exposure could lead to irritation.

Respiratory Disease

Hurricanes often displace thousands, forcing them to leave their homes and live in close quarters in shelters. This can expedite the spread of respiratory diseases due to problems like overcrowding, poor ventilation, and poor nutrition, all hallmarks of disaster shelter conditions.

The risk of respiratory disease can persist long after the hurricane has passed. A 2011 study found that children and adolescents who faced multiple environmental risks during 2005’s Hurricane Katrina experienced both upper and lower respiratory symptoms in the following years. In fact, respiratory illness was so widespread that local doctors began to refer to the symptoms as “Katrina cough.”

Wildlife Problems

You have likely seen heartwarming images of animals being saved from oncoming floodwaters, such as the video of a Texas cowboy saving his precious horse. The hurricane doesn’t just displace pets and soft cuddly animals though; flood-related natural disasters increase your risk of coming into contact with more dangerous wildlife, depending on where they strike.

The Washington Post reports that snakes are particularly dangerous, and increased water levels drive them to higher ground, which increases our risk of getting bitten. According to The Weather Channel, Texas is home to 15 potentially dangerous snake species. In addition, the Lone Star state is also home to at least two types of venomous spiders, alligators, and a number of mammals that can transmit dangerous diseases through their bite, such as possums, raccoons, and armadillos.

Those in flood-affected areas are cautioned to be wary of wild animals and do their best to keep their distance.

Mold

Lastly, Fanucchi explained that even after the waters recede, the mold left over could become a health hazard.

“It depends on the type of mold, and some people are especially susceptible while some people are allergic,” explained Fanucchi, adding that “a small percentage [of mold species] are considered toxic.”

Prolonged exposure to mold spore in an enclosed setting, regardless of the mold type or someone's allergies, can still be irritating and uncomfortable.