The Cordillera Huayhuash is the second highest mountain range in the Peruvian Andes and is important for tourism, mining, and local livelihoods. These three economic activities all share an interest in the water quality of the over 50 lakes and associated drainages that exist in the region. Water quality monitoring can help ease tensions between interests from these distinct economic sectors. This dataset reports on two rounds of water quality sampling and testing performed at 56 identified monitoring stations in 2010 and 2011. Several additional spot samples were taken in both years. At each monitoring station field measures such as temperature, pH, and conductivity were taken and samples were collected for laboratory analysis of elemental concentrations (metals and others) and field analysis of biological contamination (enterococcus). The results show contamination from mining activities, from tourism activities and from natural sources. The data is in a comma separated value (CSV) format with two flat files: "Pruebas.csv" contains the measurements of all parameters for each sample; "Estaciones.csv" contains a list of monitoring stations with geographic coordinates; "README.csv" contains the data dictionaries and other metadata (description) for both of the flat files.

Two rounds of water quality sampling and testing were performed in 2010 and 2011 at 56 identified monitoring stations in the Cordillera Huayhuash, Peru. Several additional spot samples were taken in both 2010 and 2011. The selection of monitoring stations was guided by several criteria. At least two monitoring stations were identified per watershed; one at the headwaters (slightly downstream from a trekking camp if possible) and one near the confluence with the neighboring watershed. One monitoring station was identified at the source of drinking water for each community. Additional monitoring stations were identified as potential sites of contamination from mining activities. All of the monitoring station identification met Peruvian Ministry of Energy and Mines published protocols (MEM, 1994. Protocolo de Monitoreo de Calidad de Aguas. Lima, Peru: Ministerio de Energia y Minas). Samples were collected during April and May across two consecutive years; 51 stations in 2010 and 36 stations in 2011 of which 32 stations were used both years (see stations.csv). Field measurements were made for temperature, pH, conductivity, salinity, total dissolved solids, and dissolved oxygen with two distinct field instruments (the Oakton Instruments PCSTester35 multi-parameter tester and the Oakton Instruments ExStik® DO600 oxygen meter respectively). The American Public Health Association (APHA) methods 9222 and 9230 (APHA, 2005. Standard methods for the examination of water and waste water, 21st edition. American Public Health Association, American Water Works Association & Water Environment Federation: Baltimore, Port City Press) were followed for the analysis of fecal coliforms (Enterococcus spp.) in the field. Each measured sample was filtered with a 0.45 micron gridded filter. Each filter was then incubated at approximately 44.5° C for twenty four hours on Agar specially formulated for Enterococcus growth. The number of colonies that appeared was counted and a most probable number (MPN) was calculated using the number of colonies observed and the amount of water originally filtered. In 2010 split filtered (0.45 micron) and unfiltered samples were collected for heavy metal analysis at each monitoring station and in 2011 only unfiltered samples were collected. Across both years ½ liter was used as the sample volume. The collection bottles were provided by the laboratory and were guaranteed to be clean (according to EPA protocols detailed below). The collection of samples in the field followed the EPA protocols published in each method detailed below. In 2010 the unfiltered sample was analyzed for dissolved mercury (Hg) concentrations in a laboratory in Lima (EnviroLab S.A.C) using EPA method 1631 (Cold Vapor Atomic Fluorescence Spectrometry) (EPA, 2002. Method 1631, Revision E: Mercury in Water by Oxidation, Purge and Trap, and Cold Vapor Atomic Fluorescence Spectrometry. Baltimore: United States Environmental Protection Agency). The Mercury measurement was not repeated the second year as no sample from 2010 yielded a positive result and no new sources of mercury were identified. In 2010 the unfiltered sample was analyzed for a full run of elemental concentrations (As, Ba, Be, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, Se, Tl, V, Zn, Ag, B, Bi, Ca, Fe, K, Li, Mg, Na, P, Si, Sn, Sr, and Ti) with the EPA 200.8 method (inductively coupled plasma mass spectrometry) (EPA, 1994. Method 200.8 Determination of trace elements in waters and wastes by inductively coupled plasma mass spectrometry. Cincinnati: United States Environmental Protection Agency). In 2011 the elemental analysis was narrowed to aluminum (Al), arsenic (As), cadmium (Cd), copper (Cu), manganese (Mn), nickel (Ni), lead (Pb), and zinc (Zn) based on the results from 2010.