In the 1920s, agriculture had boomed in the valley as the Imperial Irrigation District delivered large quantities of Colorado River water to irrigate the crops. The lake would have dried up naturally, but with flood irrigation being commonly used, plenty of water ran off the farms into the lake and kept it full. The district holds senior rights to water from the Colorado River according to Doctrine of Prior Appropriation, which is based on whoever first put the water to beneficial use could continue to claim it. In 1930, a wildlife refuge was established on some wetlands along the edge of the lake that had attracted many birds. The fish flourished in the lake and provided a source of food for massive populations of migratory birds. Birdwatchers flocked to this new refuge in the middle of a desert.