Recent efforts have been made to determine the environmental impact of mining over the past 11 years in the Jequetepeque River basin, in northern Peru. We have now analyzed data from two studies to elucidate the spatial and temporal trace metal distribu- tions and to assess the sources of contamination. These two studies were carried out from 2003 to 2008 by a Peruvian government administration and from 2008 to 2010 by us. We analyzed 249 samples by principal component analysis, measuring: pH, electrical conductivity, total dissolved solids, total suspended solids, chloride, weak-acid-dissociable cyanide, total cyanide, nitrite and nitrate, ammonium, sulfate, and trace metals and metalloids (Al, As, Ca, Cd, Cu, Cr, Fe, Mg, Mn, Ni, Pb, and Zn). Within the spatial distribution of the basin, the highest Al, As, Cu, Fe, Ni, and Pb concentrations were found at the closest point to the mine sites for both periods of time, with the higher peaks measured during the first years of the sampling data. Temporal trends showed higher con- centrations of Cu and Fe in samples taken before 2005, at which point the two mines were closed. Risk assessment was quantified by the hazard quotient as related to water ingestion. The risk for human health posed by the concentrations of several trace metals and metalloids was found to be highly adverse (As and Cr), significant (Al, Cd, Cu, Fe, and Pb), or minimal (Ni and Zn

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