The Williamson Watershed (HUC 18010201) is located in Eastern California and covers approximately 1,300 square miles. The hydrology of the watershed is dominated by snowmelt, which typically occurs from April through June. The snowpack in the watershed is monitored regularly by the California Department of Water Resources, and in recent years has been below average due to drought conditions. Surface water in the watershed is mostly used for irrigation and domestic purposes, with the largest reservoir being Lake Crowley. The constituents of the reservoir include dissolved solids, nutrients, and metals from agricultural and urban runoff. Interesting climatic trends include an increase in temperature and a decrease in precipitation over the past several decades, which has led to a more arid environment and increased water scarcity.