Between 1980 and 2013, Glen Canyon Dam generated an average of 4,717 gigawatt hours (GWh) per year, enough for about 400,000 homes. The highest was 8,703 GWh in 1984, and the lowest was 3,299 GWh in 2005. Power generation is affected not only by the volume of water passing through the dam, but also the depth of water in the reservoir, as a higher water level means more pressure (head) on the turbines. Hydropower generated at Glen Canyon serves about 5 million people in Arizona, Colorado, Nevada, New Mexico, Utah and Wyoming, and is sold to utilities in these states as 20-year contracts. Power sales have been managed by the Western Area Power Administration since 1977. Glen Canyon Dam generates enough power to offset 6.7 billion pounds (3 billion kg) of carbon dioxide emissions each year. However, drought conditions in the 21st century have reduced the amount of hydropower available from Glen Canyon Dam.