Colorado flooding continues, photo by Corrieb via Creative Commons

So far, four people have been found dead and 172 remain unaccounted for, although that number is expected to continue to decline, as it has already decreased from the 218 people who were at one point missing. 

"We're assuming some of them have been stranded, we're assuming that some made their way out and simply haven't contact us or friends and family to get off the list, we're assuming that there may be further loss of life or injuries," Boulder County Sheriff Joe Pelle told CNN.

Brave rescue workers are trying to reach the hundreds of residents who have been cut off by the worst flood in decades. Search and rescue teams—and now even the National Guard—have begun using boats and helicopters to rescue residents from isolated areas where the roads have been completely demolished. 

The flood has spread over a 4,500-squeare-mile area according to the Weather Channel. Many experts are fearful because even minimal rainfall this weekend may cause flash flooding. 

““The thing that worries us the most are the things that we don’t know right now,” Boulder County Sheriff Joe Pelle said in an afternoon briefing. “We don’t know about lives lost, homes lost, people stranded in many, many of the canyon areas in our upper communities.

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