La Rinconada, in the high Andes at southern Peru, is a town heavily engaged in artisanal gold mining, where tailings and waste are dumped into streams of river headwaters. For this reason, mercury was evaluated in surface water and sediments of the Lunar de Oro stream, in its origins at the Ananea glacier. Four points were sampled in the months of December 2014, and January and March 2015. In both segments, mercury was determined by atomic fluorescence spectrophotometry (EPA 245.2), and pH, dissolved oxygen, electrical conductivity, total dissolved solids and temperature were determined by multiparameter and in laboratory. In the four sampling points, mercury in water presented similar levels, with values between < 0.00005 and 0.00043 mg/L (n = 12), although in March, related to a lower flow, higher levels were determined (0.00034 ± 0.000032 mg/L), surpassing the Peruvian standards and the Canadian Environmental Quality Guidelines (CEQG); pH recorded an average of 3.44 ± 0.12 and oxygen 2.84 ± 0.23 mg/L, values that confirmed its low quality. Sediments showed values between 9 and 373 mg/kg, with no significant differences between zones and months, exceeding NOAA and CEQG limits for 100 % of the samples. Pollution rates confirmed that the site is extremely contaminated by mercury, corroborating its high risk for public health and the ecosystems involved.