Three synoptic sampling campaigns were conducted on upper Cement Creek, near Gladstone, Colorado, under low-flow conditions. The first campaign, conducted October 2012, was part of a larger campaign to characterize low-flow water quality in the entire Cement Creek watershed. The second campaign, conducted in September 2019, was designed to quantify metal loading and identify sources of contamination along a 2.5-kilometer study reach. The third campaign, conducted in September 2020, was designed to quantify loads and sources along the same 2.5-kilometer study reach during a test closure of a bulkhead on the Red and Bonita Mine, one of the primary sources of metals within the watershed. Streamflow measurements during the 2012 campaign were conducted using Acoustic Doppler Velocimetry. A continuous, instream injection of a sodium bromide tracer was initiated at the head of the study reach two days prior to the 2019 synoptic sampling campaign and maintained throughout the duration of the campaign. Bromide concentrations were subsequently used to determine streamflow using the tracer-dilution method. Streamflow estimates for the 2020 campaign were developed using a series of sodium chloride slug additions, wherein specific conductivity readings were used as a surrogate for chloride concentration. This data release includes concentration data (inorganic cations and anions), estimated streamflow, and calculated loads for the three sampling campaigns. Tracer data for the continuous tracer injection (2019) and slug additions (2020) are also included. Calculated loads may be used to compare low flow conditions with and without contributions from the Gold King Mine (2012 versus 2019) as well as before and after closure of the Red and Bonita bulkhead (2019 versus 2020). The data release consists of a kmz file showing site locations and the following 9 tables: Table 1, Locations of sampling sites Table 2, Synoptic sampling results, October 3, 2012 Table 3, Synoptic sampling results, September 5, 2019 Table 4, Synoptic sampling results, September 19, 2020 Table 5, Iron speciation results, September 7, 2019 Table 6, Bromide timeseries, September 3-5, 2019 Table 7, Slug addition chloride data, September 19, 2020 Table 8, Slug addition results, September 19, 2020 Table 9, Spatial profiles of streamflow and metal load