The state of California has a large number of reservoirs. Many, though not all, of these are publicly accessible in parks and recreation areas, and these lakes contribute significantly to the state's beauty, as many of them are set in the Diablo Range and the Sierra Nevada.
California's climate is Mediterranean, with most rain and snow falling in winter across much of the state; and in many populated regions such as Sacramento and the Bay Area, summer precipitation is almost unheard of, while winter precipitation is abundant. Therefore reservoirs are necessary to support California's large and rapidly growing population throughout the year.
Winter precipitation, which falls as snow in the Sierra Nevada and as rain in the Diablo Range, accumulates into rivers and creeks in canyons and valleys. Rivers flowing from the Sierra Nevada ultimately lead to the San Joaquin Valley and from there to the Sacramento Delta, while those from the Diablo Range drain into the San Francisco Bay via the Alameda and Coyote Creeks. City governments such as those in San Francisco and Los Angeles recognized the need for water and, despite environmental concerns, built dams (therefore forming reservoirs) on these rivers and creeks for the purpose of water storage. Complex underground canals, such as the Hetch Hetchy Aqueduct, along with canals in the Central Valley, brought water from the new rural reservoirs to major cities. One of the most beautiful valleys in the U.S., Yosemite Valley's neighbor and former twin Hetch Hetchy was one of the most significant casualties of this surge in development, and today the valley has been replaced by a reservoir, although the scenery around the lake remains picturesque.
Increased urbanization of the south and western portions of the state, along with suburban sprawl surrounding the state's capital, caused the construction and expansion of existing reservoirs to continue, and there are few signs that the trend will end as the state's population continues to expand rapidly. Unfortunately, many canyons and valleys are no longer to be found, but in many places this has been compensated with the creation of recreation areas surrounding the reservoirs, and activities such as boating and fishing have become possible in previously dry riverbeds and temporary streams. (In the case of Los Vaqueros Reservoir, for example, water supply is not from the nearby dry canyons, but instead from the Sacramento Delta, which has a varying level of salt content. The lake/reservoir itself is ironically in a semi-desert.)Since the depth of canyons and mountain valleys makes these places ideal locations for reservoirs, California's reservoirs are found in mountain ranges or the foothills of them. The abundance of remote canyons within the Diablo Range, along with the great depth of the Sierra's canyons, valleys, along with more canyons within the foothills, has concentrated reservoirs in these areas. It would be an impossible task to list all California's reservoirs (there are so many of them), but some of the large and particularly beautiful of them are included here. Some of them are additionally significant for historical and/or meteorological context, such as Lake Oroville, which surpassed its maximum capacity due to high precipitation during a wet season, while others during the 2010s drought ran almost completely dry. Despite the fact that droughts and floods must have caused headaches for engineers and government officials throughout the many natural disasters of the state's history, many of these events' impacts and the stories of such events have been largely forgotten (with the exception of the Lake Oroville incident), and incidents that ought to be better-known may now be marked with nothing more than an inconspicuous plaque beside a flooded building.
Reservoirs in remote (or even relatively remote) wilderness areas are popular with bears, and mountain lions are known to live in wilderness regions of the state. Reservoir water levels, which when critically low can cause fines for excessive water use and other measures, can be found at the California Department of Water Resources website.