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August 11, 2023

LEADVILLE, Colo.--The U.S. Geological Survey will be conducting a dye-tracing study in Lake Fork Creek, west of Leadville, Colorado, and just downstream from the Sugarloaf Dam between August 14 - 18, 2023.  During this time, a non-toxic dye, fluorescein, will be first introduced into the Creek between 3 and 7 p.m. and will be monitored through the night as it flows downstream.

Fluorescein, a fluorescent green dye commonly used in hydrologic studies, is non-toxic and safe for the environment. The dye will be released as a continuous slow drip for approximately 4 to 10 hours at a location in Lake Fork Creek about 400 meters downstream from the Sugarloaf dam and will be monitored at downstream locations by USGS hydrologists.

Dye injection at the creek may result in a light yellow to green color visible in the river for approximately 12 to 24 hours after the dye injection. The injection will be initiated in the late afternoon to minimize coloration of the river during high-usage hours. It is expected that minimal to no change in color will be visible in the creek to the south (downstream) from Halfmoon Creek during the monitoring period.

Green fluorescein dye in a pool of water
Fluorescein dye in a prior USGS dye tracing study.

The study is part of ongoing work by the USGS and is being undertaken to potentially identify groundwater inflow locations and provide groundwater inflow estimates to Lake Fork Creek in the reach up to 600 meters downstream from Sugarloaf dam. These estimates can be used to understand input of water to Lake Fork Creek from the historic Sugarloaf mining district.

The USGS is working in cooperation with the Bureau of Land Management, the State of Colorado, Trout Unlimited, the Natural Resource Damage Trustees of the California Gulch Superfund site, and the Arkansas River Watershed Collaborative. The USGS has received permission to conduct the dye-tracing study from the Bureau of Land Management, Lake County Commissioners, Lake County Community Planning and Development, and private owners of the Lake Fork Ranch Company.

Information on USGS studies of water resources in Colorado is available at

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The USGS provides science for a changing world. Learn more at or follow us on Facebook @USGeologicalSurvey, YouTube @USGS, Instagram @USGS, or Twitter @USGS.

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