The Environmental Protection Agency (EPA) is considering establishing federal baseline water quality standards (WQS) for certain Indian reservation waters to narrow a long-standing gap in coverage of Clean Water Act (CWA) protections. Currently, fewer than 50 of over 300 tribes with reservations have WQS effective under the CWA; most of the reservations with existing CWA-effective WQS have obtained the coverage through treatment in a manner similar to a state (TAS) under CWA section 518. In advance of any potential rulemaking to address this gap of CWA coverage, EPA specifically invites comments on whether to establish such federal baseline WQS for Indian reservation waters that do not yet have WQS under the CWA and, if so, what those WQS should be and how they should be implemented. Federal baseline WQS would define water quality goals for unprotected reservation waters and serve as the foundation for CWA actions to protect human health and the environment. Such WQS, if established, would apply only to those waters not already covered by existing CWA-effective WQS and would be superseded by any WQS subsequently adopted by an authorized tribe and approved by EPA under CWA section 303(c).