Green dye is used to trace the path of a connection to a Duluth Stream .

Strange Colors in the Creeks

One of the important tools for identifying and eliminating illicit discharges and connections into the Stormwater system and ultimately in to creeks is “dye testing”. When a suspicious discharge is noticed, the source of a pipe is in question, or when Utility staff need to verify the route of a stream, storm and sanitary sewer field staff will place liquid dye or a dye pad into a source and watch for the point where it discharges. This can result in colorful creeks.

The most frequent dye color is bright green but sometimes when more than one site is being tested red or blue are also used.



The dye is not toxic, does not leave a residue and usually disappears within an hour. Occasionally dye pads are used for long term tracing and may discharge for up to several days. Because the point at which the discharge occurs cannot always be predicted, prior posting is difficult. Information from the dye testing is used to make appropriate corrections to ensure that contaminants do not enter our natural waters.

Prior to dye testing, the Police department and the MPCA are notified. If a resident sees a strange color or has a concern within the City of Duluth please contact the Utility at 730-4130.