Although the sun is finally shining, much of Colorado is still up to its knees in water and muck from the 100-year flood damage. No doubt it will be for some time. But as images of flooded fields begin to give way to pictures of people dumping water-soiled rugs and furniture from their homes, and of children happily up to their waists in mud, it’s worth asking, what exactly are we swimming in?

The answer is that we don’t exactly know, but there’s plenty cause for concern. From extensive damage to oil fields in Colorado’s Denver-Julesberg basin to the more common hazards of household and agricultural waste, the recent historical flooding has created a stew of contamination that has yet to be fully understood.

Top on the list of environmentalist concerns is damage to many of Northern Colorado’s oil and gas wells. More than 23,000 operations in the area could have been affected, according to a Sept. 16 article in the Denver Post. While industry officials assure the public that many of the wells have been shut down and that experts are working to map and evaluate damaged operations, some contamination is inevitable given the extent of flooding.

“The scale is unprecedented,” Mike King, executive director of the Colorado Department of Natural Resources, told the Post. “We will have to deal with environmental contamination from whatever source.”

The likelihood of contamination has further fueled an already vocal anti-fracking contingent, which has been concerned about the long-term effects of the chemicals, many of them undisclosed, that are used in the fracking process.

“What we immediately need to know is what is leaking and we need a full detailed report of what that is,” activist Cliff Willmeng told the Daily Camera in a Sept. 16 article. “This is washing across agricultural land and into the waterways. Now we have to discuss what type of exposure the human population is going to have to suffer through.”

The impact from flooded well fields may remain unknown until floodwaters recede. Many wells are still inaccessible and some are likely to remain so for some time, according to a Colorado Oil and Gas Conservation Commission statement in the Daily Camera. Until resources are freed up and the weather cooperates, the status of many wells will remain a mystery.

The state of some other operations in the flood zones is more clear, however. Releases from 10 different sites were being tracked by state and federal regulators as of Thursday afternoon, including more than 5,000 gallons of an oil and water mixture, called condensate, into the South Platte River near Milliken, and about 13,500 into the St. Vrain River in nearby Firestone. Oil booms could be seen from the air, according to the Denver Post, but it’s unclear what type of clean up will be possible in the fast moving water.

Contamination from gas and oil fields is hardly Colorado’s only environmental concern. Other potential dangers include heavy metal releases from mining operations in the Four-Mile Canyon burn scar area, spent nuclear fuel stored near Platteville, and fly ash runoff near Valmont Butte, according to the Boulder Weekly.

It’s also unclear if a dam breach on Sept. 12 at the Rocky Mountain Arsenal National Wildlife Refuge—considered one of the nation’s most contaminated superfund sites—will have any far-reaching impact. Neither the EPA, the Colorado Department of Public Health and the Environment, nor the U.S. Army, which owns the refuge, have released statements regarding possible contamination.

Even short of the most critical threats, many Coloradoans are likely to come into contact with more perennial toxins in the flood’s aftermath. For instance, chemical fertilizer and pesticides from agricultural runoff, as well as raw sewage overflows, mold, and infectious diseases are all risks, according to the CDPHE. Risk of disease is especially high in communities whose water treatment and sewage centers have been flooded. Some towns have issued water boil advisories.

Although the extent of contamination remains to be seen, the bottom line for now is that people should steer clear of floodwaters whenever possible. And, needless to say, keep kids out of the mud—inside or out.