Page:John Sturgeon v. Bert Frost, in his official capacity as Alaska Regional Director of the National Park Service.pdf/19

Rh Cappaert, 426 U. S., at 141. So, for example, in the cases described above, the Government could control only the volume of water necessary for the tribe to farm or the fish to survive. See Winters, 207 U. S., at 576–577; Cappaert, 426 U. S., at 141. And likewise here, the Government could protect “only th[e] amount of water” in the Nation River needed to “accomplish the purpose of the [Yukon–Charley’s] reservation.” Id., at 138, 141.

And whatever that volume, the Government’s (purported) reserved right could not justify applying the hovercraft rule on the Nation River. That right, to use the Park Service’s own phrase, would support a regulation preventing the “depletion or diversion” of waters in the River (up to the amount required to achieve the Yukon–Charley’s purposes). Brief for Respondents 34–35. But the hovercraft rule does nothing of that kind. A hovercraft moves above the water, on a thin cushion of air produced by downward-directed fans; it does not “deplet[e]” or “diver[t]” any water. Nor has the Park Service explained the hovercraft rule as an effort to protect the Nation River from pollution or other similar harm. To the contrary, that rule is directed against the “sight or sound” of “motorized equipment” in remote locations—concerns not related to safeguarding the water. 48 Fed. Reg. 30258 (1983). So the Park Service’s “public lands” argument runs aground: Even if the United States holds title to a reserved water right in the Nation River, that right (as opposed to title in the River itself) cannot prevent Sturgeon from wafting along the River’s surface toward his preferred hunting ground.