Citizen suit plaintiffs must serve a 60-day notice letter on the alleged violator, EPA, and the relevant state agency before filing, giving regulators an opportunity to act first. The suit is barred if the government has already commenced and is diligently prosecuting a comparable enforcement action, reflecting Congress's preference for citizen suits as a backstop to, not a replacement for, agency enforcement.

Civil penalties recovered in a successful citizen suit are payable to the United States Treasury rather than to the plaintiff, which distinguishes the provision from a conventional damages claim; the practical incentive for plaintiffs instead comes from injunctive relief and the Act's fee-shifting provision, which allows recovery of litigation costs including reasonable attorney and expert witness fees for a prevailing or substantially prevailing party.

Standing requires the plaintiff to show a concrete injury tied to its use or enjoyment of the specific waterbody affected by the alleged violation, which makes the geographic and recreational nexus between plaintiff and discharge a frequently litigated threshold issue. A Juricratic simulation can model the strength of that standing showing, the diligent-prosecution bar, and the underlying exceedance evidence as separate dials to rehearse how a citizen suit's threshold and merits exposure interact.

Citizen suits are commonly filed by environmental advocacy organizations against industrial or municipal dischargers with a pattern of permit exceedances documented in publicly available monitoring reports, with litigation often settling through a consent decree that includes injunctive compliance measures and a supplemental environmental project in lieu of a larger penalty.