French officials say Swiss army helicopters made a surprise cross-border incursion into France — for the sake of thirsty Swiss cows.

The aerial operation to scoop up water caught authorities responsible for Rousses Lake in the Jura mountains by surprise. The helicopters also startled swimmers and fishermen enjoying the beaches of the lake, in eastern France.

Deputy mayor of the Les Rousses commune Christophe Mathez said Monday officials had "no idea this operation would occur" — and that the Swiss gave no warning before descending Thursday to take lake water.

Swiss authorities did not immediately comment but the military has been pumping water for livestock from Swiss lakes for a week. Thirsty cows produce less milk, of particular concern in the cheese-happy mountainous Jura region of France and Switzerland.