Good management of our lakes, rivers and estuaries requires understanding of how they work, predictions about future conditions and informed choice about actions to get the outcome the community wants.

MidCoast Council and Department of Planning and Environment (DPE) have worked together to put these principles into action.

International best practice suggests that research, modelling, management and monitoring should all use the measures of condition and success. DPE research allowed the development of a solid understanding of the impacts of catchment activities on lake health. It also concluded that abundance of algae and water clarity would be good indicators for the future.

Council used this scientific understanding to form the Water Quality Improvement Plan in 2009, which was designed to achieve a number of specific outcomes, expressed in terms of water clarity and algal abundance. Progress towards these outcomes has been measured using the same measures in the annual report cards.

The MidCoast Council community value the health of our waterways, and the Waterway and Catchment Report Card is a tool that Council use to monitor how we are tracking.

DPE have undertaken an ecological health monitoring program in Wallis Lake and Khappinghat as part of the state-wide Monitoring, Evaluation and Reporting Strategy (MER). As part of the strategy, these estuaries were selected as two of seven across the state to be sampled each year to track inter-annual variability in two ecological health indicators; chlorophyll a (the amount of algal growth in the water) and turbdity (the amount of sediment in the water).

Since 2011 the monitoring program has been expanded to cover other key sites across the MidCoast Council area. DPE have provided an independent scientific evaluation on the ecological health of Wallis Lake, Smiths Lake, Karuah River Estuary, Khappinghat and the Manning River Estuary.

In 2022 an additional three sites were added in the Manning River Estuary, following recommendations from the Manning River Estuary and Catchment Program.

Ecological health does not refer to environmental health issues such as drinking water quality, safety for swimming, heavy metal contamination, disease, bacteria, viruses or our ability to harvest shellfish or fish.

The monitoring program has assessed the Ecological health of Wallis and Myall Lakes, Manning and Karuah River Estuaries and the Khappinghat Estuary. There are a number of steps taken to determine the score for each zone and subsequent Report Card grade:

• Selecting the indicators.
• Identifying the guideline values
• Collecting the data.
• Calculating the zone score.
• Allocating the Report Card grade.

Selecting the indicators

Chlorophyll and turbidity were chosen as the indicators as they are proven to be very informative and responsive measures.

What we do on the land impacts on the quality of water that runs off. If the quality of the runoff is poor it puts stress on the environment. Stressors are changes to the environment that result from activity; these can lead to ecological harm. Stressors can include nutrients, acid leachate and sediment in the water (turbidity).

Ecological condition grades are a combination of turbidity (water clarity) and algae (measured as chlorophyll a) scores.

Using the guideline values

A healthy ecosystem has an expected range of diversity and function which supports the environmental values and community uses of the waterway. Water quality monitoring is used to determine if the environmental value of (healthy) aquatic ecosystems is being met. Indicators (e.g., chlorophyll, turbidity) are selected based on a potential issue (e.g., excessive algal growth, excessive sediment in the water) that may pose a risk to the environmental value (e.g., aquatic ecosystems) being assessed. Guideline values for indicators have been derived from extensive monitoring of different estuary types in New South Wales and are based on data from pristine (reference) sites.

Guideline values may be given as a threshold value or as a range of desirable values for the indicator. Where an indicator (e.g., chlorophyll concentration, turbidity) is below the threshold (guideline) value, the risk to the protection of the environmental value (aquatic ecosystem) is low. Where an indicator is higher than the threshold value there may be a risk that the environmental value will not be protected, and further investigation may be required to determine the cause of the exceedance of the guideline value.

Guideline values are specific to different estuary types (e.g., lake, river, lagoon, creek) which each have specific physical forms and characteristics. In this study, Wallis Lake, Pipers Creek, Charlotte Bay, Bombah Broadwater and Myall Lake Estuary were classified as ‘lakes’; Mid Wallamba Estuary, Karuah Estuary, Wallamba Cove, Dawson River Estuary, Lansdowne River Estuary, Ghinni Ghinni Creek, Farquhar Inlet, The Branch Estuary, Lower Myall Estuary and Upper, Mid and Lower Manning River Estuaries were classified as ‘river estuaries’ and Khappinghat Creek was classified as a ‘lagoon’. For river estuaries, guideline values for turbidity and chlorophyll change depending on the salinity of the system at the time of sampling (Table X). This is because turbidity and chlorophyll concentrations are affected by catchment runoff after rainfall as more nutrients and sediments enter the waterway.

Table X Revised Guideline Values for turbidity and chlorophyll in NSW lakes, lagoons and rivers (OEH 2018) derived from the 80^th percentile of data collected at reference in the NSW estuary monitoring program.

Collecting the data

The MidCoast Council region has been divided up into six different reporting zones.

Samples were collected on six occasions between summer and autumn from November to April. This represents the part of the year when the highest chlorophyll concentrations are expected.

At each of the selected sites, samples were taken in accordance with the New South Wales Monitoring, Evaluation and Reporting protocols.

Allocating the Report Card Grade

Defining the Report Card grade is an important step in the development of the Report Card. The grade definitions below are linked to the environmental values outlined above and are structured to allow easy comparison between each system and over time.

It is important that the cut-off values for each grade reflect the condition of each zone in comparison to a broader scale of condition across all New South Wales estuaries (i.e. an ‘Excellent’ grade represents an excellent condition for a New South Wales estuary).

To assist with the derivation of cut-offs, scores were calculated for 130 zones across a wide range of New South Wales estuaries using the same triggers and worst expected values as the MidCoast analyses. Cut-offs were then defined as representing a percentage of the scores for the state.

For example, a zone score less than 0.07 defined the 20% of best zone scores in the state and this became our ‘Excellent’ grade. We did not use a score of 0 as ‘Excellent’ because, as a consequence of how the trigger values are calculated, we expect that even pristine reference sites will exceed trigger values 20% of the time.