When California gained statehood in 1850, its official water policy was based upon riparian rights. These stated that property owners had the right to the use of water from any waterway that bordered their land. This official system conflicted with the one gold miners and settlers developed, which was known as “first in time, first in right.” This granted water rights to the first person to claim ownership of a waterway. Over time, this system became known as appropriative rights; where water ownership is based upon physical control of a waterway and its “reasonable and beneficial” use by a party. Nowadays, both of these systems exist, and often find themselves in conflict.

In 1886, California’s Supreme Court ruled in Lux v. Haggin that appropriative rights were secondary in status to riparian rights. In 2020, California’s third District Court of Appeal ruled in Modesto Irrigation District (MID) v. Tanaka that Tanaka had riparian rights to divert water from the Middle River to use on her agricultural land, dating back to the original purchase of the land in 1890. The court refused to recognize the appropriative rights to the river water that MID was claiming.

Under the California Constitution, “beneficial use” of water is for; irrigation, recreation, hydroelectric power, residential supply, municipal and industrial supply, and protection/management of fish and other wildlife. As the unpredictable and volatile nature of California’s water supply has become recognized, especially with recent droughts and floods, disputes over water allocations have grown. In land-use decisions, availability of water is often a decisive issue, as state laws require that developers prove that enough water is available to sustain their projects. 

Projects to collect and store water have also been contentious. A plan to create a tunnel underneath the Delta, drawing Sacramento River water to the head of the California Aqueduct is opposed by environmentalists on the grounds that it would negatively affect the water quality of the Delta. The Sites Reservoir in Colusa and Glenn Counties, which has been proposed and planned for over seven decades, has only recently begun the process of construction after passing an environmental impact review.