Heavy rainfall increases the flow of sediment into our local streams and creeks, increasing the cloudiness. As a result of heavy rainfall over the Four Mile burn area, this sediment has been significant, contributing to a temporary discoloration of Four Mile and Boulder Creeks. The cloudiness and discoloration is an indicator of poor water quality and can mean an increased level of pathogens, such as E. coli and Giardia. People should always avoid drinking untreated and unfiltered water from streams, creeks, lakes, etc. Cloudy fast moving water may also have hidden debris that poses a safety risk, so people should avoid recreational activity in the creeks after heavy rainfalls or at a minimum exercise extreme caution.

Treatment plants for drinking water are designed to remove sediment and disinfect the water against pathogens, so the cloudy stream is not a concern for tap water. The city of Boulder does not draw any of its drinking water from these creeks.