No Halloween prank: Fraser River will turn green Monday for groundwater study

GRAND COUNTY, Colo. — If you take a stroll along the Fraser River on Monday afternoon, you may notice that the normally clear water is now yellow-ish, or even a bright green.

Grand County

This is all part of a dye-tracing study, led by the U.S. Geological Survey (USGS) Colorado Water Science Center .

Researchers will begin a continuous slow drop of an environmentally safe and non-toxic dye called sodium fluorescein into the river near Confluence Park in Winter Park between 3 p.m. and 7 p.m., and will monitor it as it flows downstream.

Grand County Government

The study will continue through Nov. 1.

Connor Newman is a hydrologist with the USGS who was at the drop site on Monday.

"We're doing it to be able to locate groundwater inflows into the stream because many of the groundwater inflows occur along the bottom of the stream bed, where we can't see them with the naked eye," he explained.

This project will help the USGS "identify potential groundwater inflow locations and estimate groundwater contributions to the Fraser River," the organization added . "These estimates can be used to understand the sustainability of streamflow and groundwater flow under changing climatic conditions."

The odd color will last between 12 and 24 hours. Researchers said they expect little to no visible color change in the river to the south — downstream — of the confluence between the Fraser River and St. Louis Creek.

"The goal with this data is that we'd be able to provide the information to the local stakeholders, because at this period of the year, when all the snow melt has gone and there's not much rainstorms, much of the water within the river is potentially made up of groundwater," Newman explained. "And that groundwater helps to keep the river at a constant temperature and that helps maintain fish habitat, and then also helps to maintain constant flows for human usage."

Denver7

The data collected will be passed along to the water managers in the Fraser River watershed.

The Fraser River is the first main tributary river to the Colorado River within the Arapaho National Forest, according to Grand County's website . It flows past Winter Park, Fraser and Tabernash before it joins the Colorado River two miles west of Granby.

The Town of Fraser and Winter Park, Grand County and Trout Unlimited have all approved this study.

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