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AREA: 33.68 km2


The Inner Harbour is located immediately to the east of the Western Basin and is bounded by mangroves on Curtis Island and the town of Gladstone on the southern edge. Coral reefs have been recorded at Turtle, Quoin and Diamantina islands although there is little evidence that these areas have recently supported viable coral communities. There are several seagrass meadows, including one monitored seagrass meadow in the north of this zone. The Quoin Island Turtle Rehabilitation Centre is located in the centre of this zone and the Barney Point Coal Terminal is located on the south-east banks of the zone.

This zone has three water and sediment monitoring sites, one seagrass monitoring meadow, two fish monitoring sites, one mud crab monitoring site and two mangrove monitoring sub-zones.

Gladstone Healthy Harbour Partnership GHHP report card


The Inner Harbour received an overall water quality score of 0.78 (B). 

Sediment quality of the Inner Harbour was very good with an overall score of 0.93 (A).

The following graphs compare the Water and Sediment scores reported for 2023 (top line) to those from the previous year.



Very good (0.85-1.00)

Poor (0.25-0.49)

Good (0.65-0.84)

Satisfactory (0.5-0.64)

Very Poor (0.00-0.24)

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No data available

Overall, Water quality in the Inner Harbour (0.78) scored slightly lower than the 2022 report card, however, the overall grade (good, B) remained unchanged. This score was calculated by aggregating the three sub-indicator and associated measure scores (Physiochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and dissolved metals, and dissolved metals – aluminum, copper, lead, manganese, nickel and zinc).

Within the Physiochemical sub-indicator, Inner Harbour received a score of 1.00 and a very good grade (A) for pH indicating that the average pH was well below the guideline value range. This zone received a score of 0.46 and poor grade (D) for turbidity indicating that average turbidity was above the guideline value. 

Within the Nutrient sub-indicator both total nitrogen (0.61) and chlorophyll-a (0.54) had satisfactory grades (C), indicating that average concentrations for these measures were within the guideline values for this zone. In contrast, total phosphorus (0.70) received a good grade (B) as the average concentrations was below the guideline value.

All six Dissolved metals received high scores (1.00) and very good grades (A) indicating that average concentrations were well below the water quality guideline values.

For Sediment quality, Inner Harbour received an overall score of 0.93 and a very good grade (A), also a similar result to the previous year. This score was calculated by aggregating one sub-indicator and associated measure scores (Metal and metalloids – arsenic, cadmium, copper, lead, mercury, nickel and zinc).

In 2023, six of the seven Metal and metalloid sub-indicator measures received very high scores (0.93–1.00) and very good grades (A) and reflect all concentrations were well below guideline values. One measure – arsenic – received a score of 0.58 and a satisfactory grade (C), indicating that concentrations of arsenic in the Inner Harbour are within guideline value.

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Inner Harbour has one monitored meadow in the south-east corner of the zone near South Trees Inlet. Meadow 58 Seagrass scores have steadily declined over the past four years and in 2023 received the overall score of 0.10. The continued decrease in score was the result of changes in the meadow species composition with no persistent Zostera muelleri recorded in the meadow in 2023. 


No mangrove assessment was conducted in 2023, results are from monitoring conducted in 2019. The overall mangrove score for the Inner Harbour was 0.55 (C) indicating a satisfactory condition for mangroves in this zone. Mangrove extent (0.62), canopy condition (0.51) and shoreline condition (0.52) were all satisfactory.

The overall score improved from 0.43 in 2018 to 0.55 in 2019. This was one of three zones where an improved overall score was recorded. 

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Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream Acanthopagrus pacificus. The overall score for 2023 was higher than the previous year (2022: 0.51, 2023: 0.58), and remained a satisfactory (C) grade. The number of bream caught during the 2022–23 reporting period were as follows: 2022 report card: 99 fish, 2023 report card: 53 fish.

Fish health is assessed though two sub-indicators, Fish condition and Fish Health Assessment Index (HAI). 
The overall score for Fish health in 2023 was 0.81 and received a good grade (B). The 2023 results were calculated by the average of the Fish HAI score (0.90; results carried over from 2021) and new assessment of Fish condition which scored similar to the previous year (2022: 0.74, 2023: 0.73).  


The zone score and grade for Inner Harbour was not calculated in 2023, due to a small number (only four) of mud crabs caught during the monitoring period. The small sample size (less than five) means it is not appropriate to calculate grades for this zone, except for the abundance measure which scored (0.00).

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