Unbelievable videos and hard to watch images of victims from Hurricane Harvey having to wade through water is what’s been seen across the world.

Some people even having to sit in water it waiting to be rescued. How dangerous is the flood water is a question 9NEWS worked to answer.

Jon Novick, an environmental scientist with the Denver Department of Environmental Health tests areas of Cherry Creek each week.

He says when it's warm, E. coli levels are above average, but when you get a storm those numbers can jump ot 100 times higher and that’s just for an average weather event.

When talking about something as powerful as a tropical storm or hurricane, things get a little more serious.

“People who are walking in that water are being exposed to some stuff that can really make them ill,” Novick said.

Based on some of some of the images we've seen, we know being in flood water is not by choice for some.

“Your first concern is getting to safety, but if you are just walking around in it there are definitely issues with you can get infections if you have cuts or sores,” Novick said.

It's also nearly impossible to ignore the smell flood waters bring and it can come from different places.

“Wastewater treatment plants with all that rain become overwhelmed and they start to spill so some of that sewage is what you are smelling along with oil and grease,” Novick said.

Coloradans experienced massive flooding back in 2013 and scientists say the first floods were the worst.

RELATED: You donated to the Red Cross. Here's what happens next

“There were a lot of sediments, higher levels of bacteria some heavy levels of metals,” Novick said.

Still, that was just a fraction of what people in the South are dealing with.

“Rather than just being limited flooding the whole city is flooded,” Novick added.

If you have been in flood waters, scientists say to make sure you clean your hands before eating or drinking since you can become extremely sick.

Those whose homes have flooded should also check for mold.