Here's the thing, though: federal lands are administered directly by the federal government. The only avenues they have for rule-making are Congressional statut

Here's the thing, though: federal lands are administered directly by the federal government. The only avenues they have for rule-making are Congressional statutes and agency regulations. There is nothing else available to them to achieve the goal of making and enforcing a rule, because that's how they're legally set up. So to forbid washing fish at a faucet in a national park... you literally do have to make a federal law (or a regulation with the force of federal law). This is also why they have their own law-enforcement agency (the United States Park Police): Congress was, for a very long time, reluctant to authorize a general federal police force, so many agencies have their own specific police force operating solely within that agency's jurisdiction. It also creates fun inter-jurisdictional issues since the U.S Capitol building has its own separate police force, but the Capitol building is on the National Mall, which is Park Police territory.