ENVIRONMENTAL
RESULTS
ABOUT THE ZONE
Colosseum Inlet is an estuarine zone that is sheltered by Hummock Hill Island. Colosseum Inlet connects to both the Outer Harbour and Rodds Bay zones. It is outside the Gladstone Port Limits and inside the Great Barrier Reef World Heritage Area. The inlet has several large tributaries branching off the main creek and all are lined with mangroves and salt pan areas.
WATER & SEDIMENT
Colosseum Inlet received an overall water quality score of 0.81 (B).
Sediment quality of Colosseum Inlet was very good with an overall score of 1.00 (A).
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The following graphs compare the Water and Sediment scores reported for 2024 (top line) to those from 2023.
WATER
SEDIMENT
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)
No data available
Overall, Water quality in the Colosseum Inlet (0.81) scored lower than in the 2023 report card and resulted in a decline in the overall grade (good, B). This score was calculated by aggregating the three sub-indicator and associated measure scores (Physicochemical – pH and turbidity, Nutrients – total nitrogen, total phosphorus and dissolved metals, and dissolved metals – aluminium, copper, lead, manganese, nickel and zinc).
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Within the Physicochemical sub-indicator, Colosseum Inlet received a very good grade (A) for pH (1.00), and a good grade (B) for turbidity (0.75), indicating that both measures were within the guideline value ranges.
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Within the Nutrient sub-indicator both total nitrogen (0.44) and chlorophyll-a (0.37) had poor grades (D), indicating that these measures were above the guideline values for this zone. In contrast, total phosphorus (0.93) received a very good grade (A).
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All six Dissolved metals received high scores (0.94-1.00) and very good grades (A), indicating that these were well below the water quality guideline values.
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For Sediment quality, Colosseum Inlet received an overall score of 1.00 and a very good grade (A), a similar result to the previous year. This score was calculated by aggregating measure scores (Metal and metalloids – arsenic, cadmium, copper, lead, mercury, nickel and zinc).
In 2024, all seven Metal and metalloid sub-indicator measures received very high scores (1.00) and very good grades (A), indicating that they were well below the guideline values for this zone.
HABITATS
MANGROVE RESULTS
Colosseum Inlet has two Mangrove monitoring zones – one at Colosseum Creek, and another at Hummock Hill. In 2024, the overall grade for Mangroves at Colosseum Inlet declined to a satisfactory (C) from a good (B) in 2019. In 2024, mangrove extent remained a very good grade (A) at Colosseum Inlet. The grade for canopy condition at Colosseum Inlet declined from a good (B) in 2019 to a satisfactory (C) in 2024. Shoreline condition of mangroves at Colosseum Inlet declined in grade from a satisfactory (C) in 2019 to a poor (D) in 2024.
FISH & CRABS
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream Acanthopagrus pacificus. The overall grade for fish recruitment at Colosseum Inlet improved from a poor (D) in 2023 to a good (B) in 2024.