If you live, work or play in Boulder you are at risk. The city of Boulder has the greatest potential for loss of life from flash flood of any community in Colorado. This is largely due to the city’s location at the mouth of Boulder Canyon and the number of people who live and work in the Boulder Creek floodplain. Other drainage basins in Boulder County are vulnerable to flash flooding as well. Flood season lasts from April 1 to September 30, but floods can happen any time.