SI-2E (2/23/05 version)
Environmental Targets And Priorities, Stream Integrity, Stream/Watershed Components: Large Rivers


On a routine annual basis, Ohio EPA conducts fully integrated river and stream biological surveys (biosurveys) in 20-25 U.S. Geological Survey 11-digit HUC watersheds and 2-3 large rivers with an aggregate total of 400-450 sampling sites. Biological, chemical, and physical monitoring and assessment techniques are used to determine:

  • A current and thorough assessment of water quality conditions in watersheds that are scheduled for TMDLs in the near future (1-3 years);
  • The extent to which use designations assigned in the Ohio Water Quality Standards (WQS) are either attained or not attained;
The designated aquatic life uses as codified in the Ohio Water Quality Standards include:
EWH (Exceptional Warmwater Habitat)
WWH (Warmwater Habitat)
CWH (Coldwater Habitat)
MWH-C (Modified Warmwater Habitat-Channelized)
MWH-MD (Modified Warmwater Habitat-Mine Drainage)
MWH-I (Modified Warmwater Habitat-Impounded)
LRW/LRW-S (Limited Resource Water)
LWH/WWH-L (Limited Warmwater Habitat)
SSH (Seasonal Salmonid Habitat).
  • If use designations assigned to a given water body are appropriate and attainable;
  • If any changes in key ambient biological, chemical, or physical performance or response indicators have taken place over time, particularly before and after the implementation of point and nonpoint source controls;

The key to having a successful watershed approach is in using the different types of indicators within the roles that are the most appropriate for each. The inappropriate use of stressor and exposure indicators as substitutes for response indicators is at the root of the national problem of widely divergent 305(b) statistics reported between the States. This issue is discussed in the 1994 Ohio Water Resource Inventory (Ohio EPA 1995).

The principal biological evaluation tools used by Ohio EPA to determine aquatic life use status are the Index of Biotic integrity (IBI) (PDF 1164kb), the Modified Index of Well-Being (MIWB) (PDF 1164kb) and the Invertebrate Community Index (ICI) (PDF 801kb). These three indices are based on species richness, trophic composition, diversity, presence of pollution-tolerant individuals or species, abundance of biomass, and the presence of diseased or abnormal organisms. The IBI and the MIWB apply to fish; the ICI applies to macroinvertebrates. Ohio EPA uses the results of sampling reference sites to set minimum criteria index scores for use designations in water quality standards. Provisions addressing biological criteria are in paragraph (A)(6) of rule 3745-1-07 (PDF 68K) of the OAC.

Simultaneous with biological evaluation, habitat is assessed using the Qualitative Habitat Evaluation Index (QHEI). The QHEI scores help to explain:

  • Biological performance using the indices (ICI, IBI, and MIWB) above;
  • Stream morphology;

both of which explain:

  • The aquatic life use the stream is capable of supporting;

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Evaluating Large Rivers

The specific design of the Ohio EPA biosurveys are dependent on stream size. Ohio EPA defines Large River Assessment Units as one of 23 rivers (PDF 2035kb) with watershed sizes of greater than 500 square miles. Collectively the Ohio LRAUs represent 1285 miles of river mainstem. LRAUs span numerous HUC 11 watersheds. Until the LRAU approach to sampling, water quality status data for the large river mainstems was segmented into individual HUC 11 units, even though the influence of any particular contiguous HUC 11 is generally minimal. Now that the LRAU has been implemented, large rivers are considered in their entirety.

LRAU characteristics are fundamentally different both biologically and morphologically from those found in HUC 11 watersheds. Large rivers have lower stream gradients and consequently lower velocity flows under average conditions. The volume of water is larger and there are more pools and fewer riffles. Those riffles that exist are deeper. Consequently, the fish and macro-invertebrates communities are different and less diverse than those found in WAUs, because the habitat is more uniform throughout the stream reach.

All of these unique characteristics are the basis for selecting the number and location of sampling sites and interpretation of sampling results into water quality attainment status. Specifically, water quality attainment in large rivers is determined according to the linear method. The length of the river deemed to be in attainment is divided by the total length of the river to yield one value which represents the most general expression of the river's aquatic life use status.

More details are available at: