The Chulitna River basin in southwest Alaska drains an area of about 1,160 square miles, with the lower 158 square miles of the basin in Lake Clark National Park and Preserve. Water from this basin influences Lake Clark ecosystems that support salmon that, in part, sustain the Bristol Bay fishery. An area of about 391 square miles in the upper part of the Chulitna River basin has been staked for mining development (1,670 claims), and a proposed large scale copper-gold-molybdenum mine (Pebble Mine) lies adjacent to the Chulitna River drainage. The U.S. Geological Survey in cooperation with the National Park Service conducted a water-quality assessment of the Chulitna River from October 2009 to June 2012. Discrete water-quality samples and continuous-records of dissolved oxygen, pH, specific conductance, turbidity, water-stage, and water temperature data were collected from the Chulitna River. In addition, four miscellaneous sites were visited five times during 2010–12 to measure flow and water-quality parameters.