When Lagunitas Brewing Co. fills its beer bottles, Northern California’s Russian River provides the main ingredient.

Lagunitas has become one of the fastest-growing stars of California’s booming craft beer scene. But the Russian River is shrinking after three years of punishing drought.

“We are at the maximum growth threshold here in California because of water,” said Leon Sharyon, chief financial officer for Lagunitas, which uses nearly 2 million gallons of river water a year at its Petaluma brewery.

Breweries run through an average of four to seven gallons of water to end up with one gallon of beer. With California in the midst of a water crisis, breweries are scrambling.