In an age of vitamin waters and energy drinks, the decades-long decline in U.S. milk consumption has accelerated, worrying dairy farmers, milk processors and grocery chains.

The industry "is coming to recognize this as a crisis," says Tom Gallagher, CEO of Dairy Management Inc., a farmer-funded trade group that promotes milk products. "We cannot simply assume that we will always have a market."

Per-capita U.S. milk consumption, which peaked around World War II, has fallen almost 30% since 1975, even as sales of yogurt, cheese and other dairy products have risen, according to U.S. Department of Agriculture statistics. The reasons include the rise in popularity of bottled waters and the concern of some consumers that milk is high in calories.

Another factor, according to the USDA, is that children, who tend to be heavy milk drinkers, account for a smaller share of the U.S. population than they once did.

To revive sales, milk companies and retailers are pushing smaller, more-convenient packages and health-oriented varieties, including protein-enhanced milk aimed at fitness buffs.

For more, see: America's Milk Business in a 'Crisis'