The Boulder watershed (HUC 10020006) is located in the Colorado Rocky Mountains and has a land area of approximately 376 square miles. The hydrology of the watershed is influenced by snowmelt, which accounts for up to 80% of the annual streamflow. The watershed experiences a high variability of snowpack from year to year. The surface water of the watershed is mainly used for municipal water supply and irrigation. The reservoirs within the watershed include Gross Reservoir and Boulder Reservoir, which are used for water storage and recreation. Interesting climatic facts include the frequent occurrence of Chinook winds, which can cause rapid temperature increases, and the occurrence of lightning storms during the summer months. There has been a trend of decreasing snowpack in recent years, which may have implications for the water supply in the watershed.