Estuary report cards

We use report cards to tell us about the condition of NSW estuaries.

The Department of Planning and Environment, in collaboration with local councils, monitors water quality and ecosystem health in estuaries across New South Wales. The results of this monitoring program are used to generate report cards, which enable us to compare water quality and ecosystem health over time.

State-wide water quality monitoring in NSW estuaries is carried out as part of the NSW Marine Estate Management Strategy.

Water quality report cards

We monitor water quality in estuaries across NSW by measuring ecosystem health indicators including:

  • abundance of algae
  • water clarity
  • a range of supporting indicators, such as salinity, oxygen, pH, temperature and suspended sediments.

These indicators tell us about the health of ecosystem processes and how the water quality might support and enhance biodiversity and habitats for each estuary.

Our Estuaries and Catchments Team develop estuary water quality report cards based on the 2 main water quality indicators: algal abundance and water clarity.

The data from our monitoring program is used to develop guideline values for relevant water quality indicators following principles outlined in the National Water Quality Management Framework. Reference systems with pristine catchments and minimal disturbance for type of estuary are sampled routinely to develop guideline values. Monitoring data is compared to the guideline values to determine the condition of an estuary over time.

A full description of how grades are calculated is available in our technical report Assessing estuary ecosystem health: Sampling, data analysis and reporting protocols.

The estuary water quality data that supports the development of the report card grades is available on our SEED data portal. This assessment does not measure human-use environmental issues such as drinking water quality, safety for swimming, heavy metal contamination, disease, bacteria, viruses, or ability to harvest shellfish or fish.

What the grades mean

Crooked River water quality report card for algae and water clarity showing colour-coded ratings (red, orange, yellow, light green and dark green, which represent very poor, poor, fair, good and excellent, respectively). Algae is rated 'good' and water clarity is rated 'good' giving an overall rating of 'good' or 'B'.

A healthy estuary has clear water and low levels of algal growth. Each water quality report card gives an overall grade for the health of an estuary for a specific year based on combined measurements of water clarity and algal abundance.

The grades range from A (excellent health) to
E (very poor health):

  • A – excellent
  • B – good
  • C – fair
  • D – poor
  • E – very poor.

Algae are a diverse group of mostly aquatic plants that include microscopic algae found in waterways. We measure chlorophyll a, a pigment that gives plants their green colour, to get an indication of how much algae is present in a water sample.

Algae can grow quickly when high levels of nutrients such as nitrogen and phosphorous are present in a waterway. Nutrients can enter an estuary through urban stormwater, agricultural runoff, sewage and sediment runoff from the land. The amount of light, water clarity and water temperature also influence the abundance of algae in a waterway.

This growth can cause an ‘algal bloom’ which can reduce the amount of light available to aquatic plants and animals. The algae eventually die and are eaten by bacteria, which removes oxygen from the waterway and potentially harms other species; for example, fish kills.

Low levels of algae usually indicates that low levels of nutrients are entering a waterway; thus, a ‘good’ grade for algae, means a suitable amount of nutrients are entering and remaining in an estuary.

Water clarity is determined by turbidity, a measure of how much material, such as sediment or organic matter, is suspended in water.

High levels of turbidity indicate that excessive amounts of sediments are present in an estuary, which equates with poor water quality. Fine sediment can stay suspended in water until it accumulates in low energy shallow areas of an estuary, like seagrass meadows. Coarser material tends to sink and settle in deeper sections of an estuary.

High turbidity can have negative impacts on aquatic ecosystems. For example, it can reduce available light which limits the ability of important underwater plants like seagrass to grow. Alternatively, low levels of turbidity and good water clarity indicate there is a suitable amount of sediment, organic matter and nutrients entering and remaining in an estuary, which equates with good water clarity and quality.