Indicator 2.6.5

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System

Water Type

Feed Dependent

Species

Indicator 2.6.5

by Contact on 8 October 2026

Requirement

The UoC shall ensure that the Receiving Waterbody (RW) has been classified per site as Type A, B or C, following the method outlined in Appendix 8 (8.5).

How Do I Interpret This Requirement?

  • The UoC should initially define the boundaries of the Receiving Waterbody (RW) based on hydrological characteristics, which determines its sensitivity to nutrient enrichment.

    • Hydrodynamically isolated embayments (HIEs) should be treated as separate waterbodies during the classification process.

  • Marine waterbodies include:

    • Off-shore and inshore coastal systems.

    • More enclosed waterbodies susceptible to seawater intrusion through tidal exchange or storm surges.

    • Exposed near-shore waterbodies (i.e. not in a bay or channelised system) and offshore waterbodies will be classified as Type C.

    • Once the boundaries of the RW are defined, HRT should be calculated unless the RW is an exposed near-shore or offshore waterbody.

      • The area and average depth of the waterbody need to be determined.

    • The cross-sectional area of the waterbody outflow or channel is required to calculate flow rate.

    • A transect should be determined from one side of the outflow/channel to the other side.

      • The length (in metres) of the transect is multiplied by the average depth of the transect to determine the cross-sectional area.

      • The cross-sectional area in then multiplied by the flow velocity (V). The result of this calculation is the flow rate (Q).

      • If a marine waterbody has HRT ≥5 days, it is a Type A, if it is ≤ 5 days, it is Type C.

    • Determining flow rate and levels of Total Suspended Solids (TSS) will distinguish between Type B and C freshwater bodies.

    • Flow rate can be obtained from regulatory bodies. Low flow then needs to be calculated by plotting the cumulative distribution of the data and calculating the 25^th^ percentile of the cumulative distribution.

    • This can be calculated in Microsoft Excel using the cumulative distribution function. The 25^th^ percentile (or quartile) can then be calculated.

  • Waterbody types designated under national legislation should be used only if the following are met:

    • The classification includes area-based water quality monitoring.

      • Targets are used to determine good ecological status. An example is the Water Framework Directive.

Evidence of Implementation

  • A map of the Receiving Waterbody, which outlines:

    • The area and average depth of the waterbody; and,

      • The location where flow rate (Q) was determined; or,

    • That the site is in a RW which is an exposed near-shore or off-shore marine RW (Type C only).

    • The waterbody classification, which includes outputs from HRT, flow rate and TSS calculations.

      • The methods used to measure flow rate and TSS, in accordance with Appendix 8 (8.5 and 8.12).

      • If applicable, evidence that demonstrates alternative methodologies to calculate TSS or flow rate are equivalent to the ones in Appendix 8 (8.5).

Auditors Should Confirm

  • A map has been presented by the UoC which outlines the RW, and which supports the classification of the RW.

  • The results of the HRT calculation and flow rate/TSS measurements conducted by the UoC.

    • These results will support the RW classification determined by the UoC.

  • Evidence presented by the UoC, demonstrating the methods used to measure flow rate and TSS, in accordance with Appendix 8 (8.5 and 8.12).

Useful Resources

[Steps to determine whether the RW is a HIE are as follows:]

1. If the site is in a waterbody that has been identified as a HIE by a regulatory body, this will form the boundaries of the RW.

2. Review the characteristics of the RW and determine if at least one of the following is identified:

  • The RW has poor connectivity to deep offshore waters, and/or;

  • The RW is sheltered from energetic conditions e.g., inflows, currents, exposure to onshore or monsoonal winds, and/or;

  • The hypolimnion is periodically or permanently poorly flushed.

> Where the RW shares these characteristics, it is possible to demonstrate the RW is not a HIE. The steps to demonstrate that the RW is not a HIE are as follows:

1. Identify the narrowest point in the embayment opening (red line in Figure 1).

2. Establish two transects of length, which start at the narrowest point and extend in and out of the embayment (red dashed line in Figure 1).

3. Collect water samples at 0.5m depth from an equal number of equally spaces sites in each transect.

4. Analyse water samples for concentrations of chloride, conductivity, salinity, TN or TP. Analytical methods for TN and TP can be found in Appendix 8 (8.12).

5. Plot the concentrations of the parameter analysed in step 4 against their position on the transects.

6. Based on the results from step 5, determine whether there is a statistically significant increasing or decreasing trend in concentrations moving from the furthest offshore to the most enclosed site.

7. An embayment is hydrologically isolated when a statistically significant increasing or decreasing trend in concentrations has been determined.

Figure 1. Tracer sampling points along a transect for HIE determination.