Freshwater and Estuary – What’s in a Grade?

Our results aren‘t simply pulled out of the sky, they have been prepared using a set of formulas and scores that are applied from the individual sample level all the way to the Basin grade. All of these steps and their application are based on best available science along with the expert knowledge and guidance of our science panel.

Freshwater catchments and Estuary

The freshwater and estuary reporting areas are assessed using indicators, thresholds and a normalising formula.

No Data

grade-n Sometimes there are no data available to assess an indicator. When this is the case a grey N icon is displayed.

Imputed Data

gradeX In some reporting years data are not available for an indicator in one catchment, although they have been available in the previous reporting years. In this case the score is marked with an X and is exchanged with a calculated score.

This calculated score is the previous year’s score for the indicator, which has been adjusted by the average % change at the basin scale, using these steps:

  • Compile all site results for the indicator across all the catchments of the Fitzroy Basin.
  • Remove any sites which don’t have data for both the current year and the previous year.
  • Calculate the Fitzroy Basin average score for the indicator for the current year and for the previous year.
  • Calculate the % change in score between the previous year and the current year.
  • Apply this % change to the indicator score that was the previous year’s score in the catchment with the missing data.
  • Use the calculated value to score the indicator for the catchment.

How are Grades Awarded?

How the Basin is scored

How the Reporting areas are scored

Indicator categories have a weighted average applied to them. You can see the break-down below.


Freshwater indicators categories include physical/chemical parameters, nutrients, toxicants and ecology. There are a range of indicators within these categories which measure important aspects of ecosystem health. Together they contribute to a holistic picture of waterway health in the Fitzroy Basin.  Each of the indicator categories contributes a certain percentage towards the overall reporting score.

Physical & Chemical

Physical–chemical parameters (often called phys-chem) include:

  • Conductivity – Measuring the ability of the water to conduct electricity provides information about the concentration of dissolved solids that are present. Higher conductivity equates to higher dissolved ions or salts which make the water more saline. Freshwater contains less salinity than the estuary or marine zones.
  • pH – pH is a measure of acidity or alkalinity. In water, a neutral pH (pH value of 7), which is neither acidic nor alkaline, enables life to thrive.
  • Turbidity – This is a measure of the amount of sediment, dirt, organic material and other matter suspended in waterways. Water clarity allows light penetration for aquatic life to grow. Suspended sediment may also contribute to other physical and chemical interactions in waterways.
  • Sulfate – Dissolved sulfate concentrations interact with other physical-chemical components in waterways as well as nutrients which can negatively impact aquatic life and water toxicity.

The individual physical and chemical properties of the water can vary considerably and each of the parameters interact and can impact the other. For example, pH and conductivity can both be influenced by the temperature of the water.


Nutrients are important for plant and animal life to thrive; however excess nutrients cause imbalances in the system which can negatively impact aquatic life and water toxicity. Nutrient parameters include:

  • Nitrogen
  • Phosphorous


Toxicant parameters include dissolved metals. Whilst many of these are essential for life, in high concentrations, some can be toxic to aquatic life.

  • Arsenic (As)
  • Aluminium (Al)
  • Boron (B)
  • Cadmium (Cd)
  • Chromium (Cr)
  • Cobalt (Co)
  • Copper (Cu)
  • Iron (Fe)
  • Lead (Pb)
  • Manganese (Mn)
  • Mercury (Me)
  • Molybdenum (Mo)
  • Nickel (Ni)
  • Uranium (U)
  • Zinc (Zn)
  • Selenium (Se)


The Ecology category includes three indicators with a range of sub-indicators:


Aquatic macroinvertebrates are animals without a backbone, such as insects and freshwater mussels, which can be seen without a magnifying glass or microscope. The macroinvertebrate score is made up of indices which measure species diversity and sensitivity.

PET Taxa richness – Macroinvertebrates belonging to the PET (EPT) Orders – Plecoptera, Ephemeroptera, and Trichoptera are particularly sensitive to changes in their environment. This index counts the number of species within the PET Orders present.

SIGNAL index – The SIGNAL Index (Stream Invertebrate Grade Number – Average Level) measures the level of tolerance and sensitivity to poor water quality of each taxa present.

Taxa richness  – This is a count of the overall species diversity.

Freshwater Fish

The Freshwater fish indicator measures species populations and diversity. It is made up of 7 sub-indicators which result in the freshwater fish index score (out of 100):

Species Composition

  • Percentage of Atheriniformes – Atheriniformes is an Order of native fish which is sensitive to water quality and habitat conditions. This measures the percentage of Atherinformes in community composition.
  • Number of Atheriniformes – this is a count of Atheriniformes species observed.
  • Percentage of Clupeiformes and Hypseleotrids – Clupeiformes and Hypseleotrids are Orders of freshwater fish which are highly tolerant to poor water quality and habitat condition. This measures the combined percentage of Clupeiformes and Hypseleotrids in community composition.

Species Diversity

  • Shannon Diversity – Shannon Diversity gives a numerical measure of species diversity, taking into account both the number of species and abundance of each species. Shannon Diversity results above 0 indicate more than 1 species present, results of 2 or more indicate a diverse freshwater fish community in the Fitzroy Basin.
  • Chao 1 Estimator – The Chao 1 Estimator accounts for unobserved species, it works on the basis that the more rare species observed, the more likely there were also unobserved species present. Chao 1 Estimator results above 6 indicate high likelihood of unobserved rare species occurrence.
  • Introduced Species – Introduced fish species pose a threat to native fish communities. They are also often found in ecosystems with poor water quality and habitat condition.

Trophic Composition

  • Percentage of Omnivores – Omnivores are found in waterways with diverse fish communities, good habitat condition and water quality.

Habitat Condition

Habitat Condition is assessed using the QLD AUSRIVAS habitat rapid assessment tool. This results in an indexed score across 9 categories. These categories assess various important components of stream habitat condition:

  • Bottom substrate/ available cover (score out of 20)
  • Embeddedness (score out of 20)
  • Velocity/depth (score out of 20)
  • Channel alteration (score out of 15)
  • Bottom scouring and deposition (score out of 15)
  • Pool/riffle, run/bend ratio (score out of 15)
  • Bank stability (score out of 10)
  • Bank vegetative stability (score out of 10)
  • Streamside cover (score out of 10)


Estuary categories are the same as freshwater, except without toxicants. The Physical/Chemical, Nutrient and Ecology categories contribute 53.3%, 13.3% and 33.3% respectively towards the overall estuary score.


Marine condition for the Fitzroy is available via additional information and does not contribute to the overall score for the basin. The marine condition report is provided by the office of the great barrier reef. It utilizes its own set of category weightings and thresholds and does not affect Fitzroy Partnership’s ecosystem health report card results.

How Monitoring Sites are scored

A flow weighting is applied to catchment indicator grades when they are averaged up to a category grade.

Formula, Indicators and Thresholds

Assessment Formula

If a sample result for an indicator is better than the benchmark, it scores 100 which is an A. If the sample result is worse than the worst case scenario (WCS) it scores a 0 which is an E. If a sample result is between the benchmark and the WCS, the score is calculated using the formula:formula
This formula standardises the sample result in to a score between 0 and 100, and is based on the formula used in and developed by the South East Queensland Ecosystem Health Monitoring Program.

Indicators and Thresholds

The following table shows all the indicators for the freshwater and estuary reporting areas and the benchmarks and worst case scenarios used in calculating the grades. Use the drop-down menu to change the reporting area.[indicator_threshold_table] (1) All metals are dissolved except Selenium, which is Total (due to no guidelines for dissolved).
(2) WQG = Water Quality Guideline or other benchmark.
(3) WCS = Worst Case Scenario.
Click here to download table as an Excel workbook