MITCHELL, Neb. — For farmers battered by floods and blizzards and one of the rainiest springs on record, this has been a year tainted by too much water.

But suddenly, across more than 100,000 acres of Nebraska and Wyoming, there is no water to be found. The dirt is cracking. The beans are turning a sickly yellow. And the corn, which looked so promising just two weeks ago, is straining for fluid through long, scorching days.

The countryside is suddenly parched because a century-old tunnel that carries irrigation water across more than 100 miles, from Wyoming to Nebraska, collapsed this month. The cause of the collapse was not yet clear but the effect has been immediate:

A large expanse of farmland is parched. And hundreds of farmers, already reeling from years of low grain prices, are without water at the most critical point of the growing cycle.