Water-quality data for the Clark Fork and tributaries in the upper Clark Fork Basin, Montana, October 2023-September 2024

Water was sampled in streams from Butte to near Missoula, Montana, as part of a long-term monitoring program in the upper Clark Fork Basin. The sampling program was completed by the U.S. Geological Survey (USGS), in cooperation with the U.S. Environmental Protection Agency, to characterize aquatic resources in the upper Clark Fork Basin and monitor trace elements associated with historical mining and smelting activities. Sampling sites were on the Clark Fork and a subset of its tributaries. Water samples were collected periodically at 22 sites from October 1, 2023, through September 30, 2024. Water-quality data included onsite stream properties and laboratory determination of concentrations of major ions, dissolved organic carbon, nitrogen (nitrate plus nitrite), ammonia, trace elements, and suspended sediment concentrations in stream water samples.