Editors' Summary: The number of citizen suits brought by environmental groups under the Clean Water Act against companies that have allegedly violated the terms of their NPDES permits has increased dramatically in recent years. Spurred in part by district court decisions that have found defendants liable for violations of the Act solely on the basis of the data reported in the permittees' own discharge monitoring reports, environmental groups have scored several stunning victories. The author reviews the large body of case law that has emerged from the flood of Clean Water Act citizen suits, including judicial response to the most commonly asserted defenses raised by the permittees. In light of the general lack of success of these defenses, the author concludes that permittees must diligently perform their monitoring and reporting obligations.