Normally the cargo moving through the Sacramento-San Joaquin River Delta contains expensive commodities meant for ports all around the world, but in drought-riddled California the most indispensable freight is currently destined for the river bottom.

Tugboats pushing and pulling barges loaded with boulders have suddenly become key performers in the state’s battle with a rapidly expanding drought, delivering supplies needed to reinforce California’s buckling water system. Around the clock crews dump the expensive cargo into the river strategically, racing to block salty tidal flows from the water pumps that sustain billions of dollars worth of crops hundreds of miles away.