Average Watershed Score

The first assessment prong involves the average statewide watershed score based on scores available for the subset of Ohio's 331 11-digit Hydrologic Unit Code (HUC-11) watersheds [PDF 437K] for which we have adequate, up-to-date data.

WAU scores reflect the relative proportion of monitoring locations within the watershed where Ohio's biological criteria were in full attainment of the designated aquatic life use. Watersheds with scores of 100 are those where all sampling locations were achieving or exceeding Ohio's biological criteria benchmarks. Conversely, those WAUs with scores of 0 reflect watersheds with severe water quality and/or physical habitat impairments and where no site met biological criteria thresholds.

Because of the innovative approach to watershed monitoring and assessment, which began in earnest in the late 1990s, the average watershed score based on the status of WAUs will serve as the benchmark for which to compare future watershed improvements as total maximum daily loads (TMDLs) are implemented and best management practices (BMPs) are put into practice on the landscape.

The maps below show WAU scores from the 2008 Integrated Report (reflecting 10 years of data up to 2006), as well as those from the 2006 Integrated Report, 2004 Integrated Report, and 2002 Integrated Report for purposes of comparison.

Large Rivers Score

The second assessment prong involves the aquatic life use attainment status of Ohio's 23 large rivers with watershed sizes greater than 500 square miles. Results of large river surveys conducted in the late 1990s are compared to similar surveys conducted in the early to mid 1980s. The measurement in this case is the actual status of river miles that are fully meeting the designated aquatic life use. These 23 Large River Assessment Units (LRAUs) represent over 1,287 miles of mainstem.

Trend assessment of the scores for the LRAUs over the past 25 years is an integral part of measuring and showing progress towards the water quality goals. The attached maps represent LRAU scores from the 2008 Integrated Report (reflecting 10 years of data up to 2006), as well as those from the 2006 Integrated Report, 2004 Integrated Report, and 2002 Integrated Report for purposes of comparison.

The Scioto River Success Story

Ohio's longest river was short on quality before federal adoption of the Clean Water Act. This graphic depicts the status and trend, over the last 20 years, of aquatic life use attainment for the Scioto River mainstem from its designated Large River Assessment Unit origin (confluence with the Little Scioto River in Marion County) to the Ohio River at Portsmouth. The tremendous turnaround in the quality of aquatic communities in the river, as reflected by the vastly improved aquatic life use attainment statistics, can be directly correlated with the expenditure of millions of dollars to upgrade and improve the quality of municipal and industrial point source discharges within the basin. More information on the Scioto River is in the Ohio EPA 1999 report Biological and Water Quality Study of the Middle Scioto River and Alum Creek. Franklin, Delaware, Morrow and Pickaway Counties, Ohio [PDF 792K].