In County of Maui v. Hawai’i Wildlife Fund, the Supreme Court held that “the statute requires a permit when there is a direct discharge from a point source into navigable waters or when there is the functional equivalent of a direct discharge.” The Court thus confirmed that some discharges traveling from point sources to navigable waters via intermediate nonnavigable and non-point- source “conduits” require permitting under the Clean Water Act. However, the meaning of “functional equivalence” was left ambiguous, and the Court’s proposed list of factors to determine functional equivalence was incomplete. This standard and its attendant factors, if applied incorrectly, risk undermining the purpose of the Clean Water Act. In this Note, I clarify that functional equivalence should be determined by the potential impact that an indirect point-source discharge can have on a navigable water. This is consistent with the Clean Water Act’s purpose and common-law origins and with judicial and regulatory history. The factors identified in County of Maui v. Hawai’i Wildlife Fund should be understood as indicia for determining an indirect discharge’s potential to impact navigable waters. Using the Clean Water Act’s public-nuisance and strict- liability roots, I also propose additional indicia that can determine whether functional equivalence holds for the purposes of permitting under different discharge scenarios.