The heavy winds and torrential rainfall from Tropical Storm Hilary have left Southern California dealing with widespread damage, and will probably still cause "catastrophic and life-threatening flooding" in portions of the Southwestern United States and the Baja California region in Mexico through Monday, according to the National Hurricane Center.

But in a part of the country that hadn't had a tropical storm hit in more than 80 years, health and safety experts are urging residents to get out of the floodwater and not swim in, touch or drink the contaminated water.

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A video shared on X, formerly known as Twitter, purportedly shows a few people in Southern California dancing, swimming in and jumping face-first into the floodwater. The video, which has been viewed tens of millions of times as of Monday morning, has brought about a consistent message from officials, health experts and journalists covering Hilary: "Please stay out of floodwater."

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"I wouldn't want to get into that floodwater right now," said Joan Rose, a Michigan State University professor specializing in microbiological water quality and public health safety.

The Centers for Disease Control and Prevention have repeatedly warned people to "stay out of floodwater," noting that it can contain downed power lines, human and livestock waste and hazardous waste among other contaminants. The wide range of contaminants can lead to wound infections, skin rash and gastrointestinal illness, the CDC says.

"What we do know is floodwater has high levels of contaminants, and the fecal content is usually high," said Rose, who holds the Homer Nowlin endowed chair in water research at MSU. "We're always concerned with any ingestion, or when people in these floodwaters touch their food, face and eyes."

Hilary, the first tropical storm to enter the region in 84 years, made landfall on Sunday over the northern Baja California peninsula of Mexico with winds of 65 mph. Hilary was at one point a category 4 hurricane off the coast of Mexico before it weakened. The storm killed a man on Sunday in Mexico's Baja California Sur, authorities said, after water swept away his car. No deaths or significant injuries had been reported in Los Angeles County as of Monday morning following Hilary, Los Angeles Mayor Karen Bass (D) said at a news conference.

Now a post-tropical cyclone, Hilary was traveling north through Nevada early Monday with maximum sustained winds of 39 mph, according to the NHC. "A brief tornado or two will be possible" in southeastern California and parts of Arizona, Nevada and Utah, the NHC said.

Flash flood warnings for the cities of Los Angeles, Glendale and Santa Clarita in Los Angeles County were extended Monday until 8 a.m. local time, the National Weather Service said in an update. More than 7 million people live in the area that was affected by the warning.

Officials in San Diego urged people on Sunday to stay inside since "the worst of the storm has yet to come." As heavy rain and dangerous flooding were pounding Los Angeles and Ventura counties on Sunday night, the NWS also warned people to not go outside.

"PLEASE STAY HOME AND OFF THE ROADS," the agency wrote on X. "This is a DANGEROUS situation."

Floodwater poses a drowning risk for anyone swimming or driving through it, but health experts say the contaminated waters also "contain many things that may harm health."

"We don't know exactly what is in floodwater at any given point in time," the CDC says.

Some of the other items that can be found in floodwater include coal ash waste that can contain carcinogenic compounds such as arsenic, chromium and mercury; debris, lumber or vehicles; and wild or stray animals such as rodents and snakes. Exposure to the contaminated waters can also lead to tetanus and leptospirosis, a rare illness from floodwater that is a bacterial disease spread through the urine of infected animals, according to the CDC.

"It is important to protect yourself from exposure to floodwater regardless of the source of contamination," the agency said. "The best way to protect yourself is to stay out of the water."

The NWS added, "Standing water hides many dangers including toxins and chemicals. There may be sharp objects under the water or the road could have collapsed."

Experts say that if people must enter floodwater, they should be wearing rubber boots, rubber gloves and goggles to protect from illness. People exposed to it should wash their hands with soap, wash all clothes that touched the contaminated waters and cover up any open wounds to prevent infection.

The country's awareness surrounding floodwater exposure has increased in the years since Hurricane Katrina crushed the Gulf Coast. The CDC determined that the number of cases of West Nile virus doubled in affected areas in Louisiana and Mississippi following the 2005 hurricane because of the mosquitoes that thrive in the presence of standing floodwater. Almost half of the inspected homes after Katrina had visible mold growth that put those residents at risk for developing respiratory problems, according to the CDC. A 2011 study of hundreds of rescued cats and dogs in the Gulf Coast after Katrina found that many of those pets had contracted infectious diseases from the floodwater.

Despite the public warnings from health officials over the years, some people have insisted on playing in it. In 2019, an Oklahoma man made light of the state's flooding in a viral video by dancing in the floodwater while Usher's "U Got It Bad" played in the background. In January, videos of people tubing, paddleboarding and "street surfing" in the San Francisco Bay Area amid flooding caused officials to urge residents to stop having fun in the floodwater, according to KRON, a San Francisco TV station.

Rose told The Post that people who insist on being in the floodwater when they don't have to be can mitigate some of the health risks. While water and rain should be celebrated by all, she emphasized that people need to be smart about willingly exposing themselves to floodwater.

"We need rain, but when it comes down in a heavy flooding situation like in California, that's when the risks get a little bit higher. They need to be careful, be cautious," she said. "You can mitigate some of the risks if you're in the floodwater, but people don't think of storm water as being as contaminated as it is."

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The Washington Post's Maeve Reston, Lori Rozsa, Ian Livingston, Maham Javaid, Paulina Villegas and Leo Sands contributed to this report.

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