San Diego could help Nevada and Arizona shore-up their water supplies under a first-of-its-kind agreement.

The deal would allow San Diego County to sell some of the rights it has to Colorado River water to the two states.

The water wouldn't physically move across state lines - instead, San Diego would draw less water from the river, leaving more available for others.

Officials say it's the first large-scale water trade between states that share rights to the Colorado River.

The agreement comes as areas of the West face worsening drought conditions - with reservoirs including Lake Powell and Lake Mead nearing critically low levels.

Details including water volumes and pricing still need to be negotiated in the agreement.

Long-term drought has reduced Colorado River system water storage to currently about 36% of capacity. 

Colorado River basin