Missouri River dye test tracked plume 41.2 miles and measured 8.2-hour delay

A river can carry a contaminant far beyond the point where it enters the water, but predicting exactly how quickly that material will travel is not always straightforward. In 2010, scientists with the U.S. Geological Survey (USGS), working with the Montana Department of Environmental Quality, conducted a dye-tracing experiment on a 41.2-mile stretch of Montana’s Missouri River to better understand how substances move through the waterway. According to the USGS report, researchers released rhodamine WT dye at two locations and monitored its movement downstream. The experiment revealed significant differences in how quickly the dye travelled through individual sections of the river, including an 8.2-hour residence time in Toston Reservoir.Tracing the river’s movementThe study focused on the upper Missouri River upstream from Canyon Ferry Lake. The researchers examined a 41.2-mile reach extending from the Missouri River Headwaters near Trident, Montana, downstream to the U.S. Route 12 Bridge near Townsend.