The legal authority for regulating wetlands comes from the Clean Water Act, which forbids the "discharge of any pollutant" into the "navigable waters of the United States." Since the late 1970s, the EPA and the Army Corps of Engineers have claimed broad authority to protect wetlands, even when they are not connected to rivers or lakes. As the Sacketts learned, putting gravel on a dry lot amounts to "discharging pollutants" into the "waters of the United States" if the lot is deemed to be wetlands.
They might get a friendlier reception from the Supreme Court. Justice Antonin Scalia once complained that the EPA has used its authority over wetlands to claim control over an "immense" area of the nation, "including half of Alaska and an area the size of California in the lower 48 states."