Red flags signal that water quality near testing sites does not meet the boating standard. The presence of fecal bacteria in water suggests contamination with sewage or feces, which in turn could mean that disease-causing bacteria or viruses are present. Most red flag days occur after heavy rainfall when stormdrains and sewer system overflows flush pollutants into the river. While it is always a good idea to wash after being on the river, it is particularly important on red flag days.
Some boaters choose to stay off the river on red flag days because of elevated bacterial levels.