The U.S. Supreme Court refused to limit the reach of the Endangered Species Act, turning away an appeal by three farms challenging the protection of a 2 1/2-inch long Northern California fish called the delta smelt.

The justices today left intact a federal appeals court decision that upheld the law as a valid use of Congress’s constitutional power to regulate interstate commerce.

The rebuff marks the sixth time the nation’s highest court has refused to question the Endangered Species Act. The latest challenge to the law had the backing of property-rights advocates, a group of California water districts and trade organizations representing farms and small businesses.

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