Ohio EPA conducts surface water quality monitoring and evaluation to determine whether or not water quality standards are being met. This means monitored streams are reassessed at least every five years. This approach was instituted in 1990 and supports activities such as the water quality standards program, National Pollutant Discharge Elimination System permitting, basic monitoring and trend reporting, NPS assessment, enforcement and litigation, dredge and fill activities, and stormwater management.
In Ohio, a "multiple lines of evidence" approach is used to identify the causes and sources of pollution associated with the observed water quality impairment. The determination relies on the interpretation of these types of data: water chemistry, sediment chemistry, habitat, effluent quality, biological monitoring, land use, and response signatures within the biological data itself. The process is akin to making a medical diagnosis in which a doctor relies on multiple lines of evidence concerning the patient's health.