The Clean Water Act (CWA) requires states to calculate total maximum daily loads (TMDLs) of individual pollutants that impair their waters. But the means by which TMDLs are calculated are imprecise, because (1) it is difficult to geographically isolate the effects of a single pollutant; (2) it is difficult to account for the effect of numerous catalysts that alter the calculation; (3) it is difficult to isolate the effects of a single pollutant source on an individual water body; (4) it can be difficult to categorize a source either as point or nonpoint; (5) extant methods fail to fully account for catalytic variables and/or assume current regulatory programs are working more efficiently than they actually are; and (6) the federal government has not allocated sufficient funds to allow state agencies to perform proper analyses. To mitigate these effects, Congress should amend the CWA to permit states to calculate TMDLs by proxy in areas in which proxies are found to be strongly correlative with water quality. This would bring clarity to interpretation of the Act and flexibility in its execution.