Tribes gained power to set water standards reaching beyond reservation borders

Evidence

In 1987, Congress amended the Clean Water Act to allow for Native American tribes to exercise sovereign authority for the purpose of tribal implementation of that act. Tribes were, accordingly, authorized to assume primary responsibility for the issuance and enforcement of permits for sources within the reservation, as well as for the promulgation of water quality standards. What made the latter especially significant was its potential application to sources of water pollution outside tribal boundaries that affect the quality of waters within them. Such extraterritorial application of tribal standards promised an injection of tribal authority into a context where disputes between bordering states and between states and the federal government had already undermined effective regulation. — Richard J. Lazarus, The Making of Environmental Law, 639