During the Water Quality Assessment process, monitoring results are compared to numerical water quality standards to determine if the water quality "measures up", for example, if it is clean enough for swimming, fishing and other uses. If water quality falls below a certain level of cleanliness, DEQ identifies the location, the parameter of concern (such as high bacteria counts) and the likely sources (such as failing septic systems or feedlot runoff). The streams that do not pass muster are listed in a widely circulated pair of reports called the 305(b) and 303(d) reports. Since 2004, DEQ has combined both the 305(b) Water Quality Assessment and the 303(d) Report on Impaired Waters into the Virginia Water Quality Assessment 305(b)/303(d) Integrated Report.

Over the long term, DEQ, in cooperation with many other state and federal agencies, must develop and implement cleanup plans to restore the health of these listed streams. The restoration plans are known as "total maximum daily loads" or TMDLs. This name is based on the total amount of pollution that can enter a stream without harming it. Visit DEQ's TMDL website for more information.