ENVIRONMENTAL
.RESULTS
ABOUT THE ZONE
Graham Creek is a mangrove-lined tidal inlet located near the south-west corner of Curtis Island. It is approximately 9 km long and flows into the southern end of The Narrows.
WATER & SEDIMENT
Graham Creek received an overall water quality score of 0.90 (A).
Sediment quality of Graham Creek 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)
Good (0.65-0.84)
Satisfactory (0.5-0.64)
Poor (0.25-0.49)
Very Poor (0.00-0.24)
No data available
Overall, Water quality in Graham Creek scored 0.90 and received a very good grade (A), similar to the 2023 report card. 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, Graham Creek received a score of 1.00 and a very good grade (A) for pH indicating that the average pH was within the guideline value range. This zone received a score of 0.92 and a very good grade (A) for turbidity, an improvement in grade from a good (B) in 2023.
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Within the Nutrient sub-indicator, total nitrogen (0.56) remained a satisfactory grade (C), while total phosphorus (0.98), improved to a very good grade (A), indicating that average concentrations for these measures were within or below the guideline values for this zone. Chlorophyll-a also improved in score (0.65) and improved from a poor grade (D) in 2023 to a good grade (B) in 2024, indicating that the average concentrations were below the guideline value.
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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.
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For Sediment quality, Graham Creek received an overall score of 0.96 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).
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In 2024, all seven Metal and metalloid sub-indicator measures received very good grades (A), indicating that average concentrations were below the guideline values for this zone.
HABITATS
MANGROVE RESULTS
Overall, Mangroves at Graham Creek improved from a satisfactory grade (C) in 2019 to a good grade (B) in 2024. Mangrove extent retained a good grade (B) at Graham Creek in 2024. The grade for canopy condition at Graham Creek improved from a poor grade (D) in 2019 to a satisfactory grade (C) in 2024. Shoreline condition was not observed at Graham Creek in 2024.
FISH & CRABS
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream Acanthopagrus pacificus. Fish recruitment scores at Graham Creek remained similar to 2023 (0.53) in 2024 (0.54), maintaining a satisfactory grade (C).
MUD CRAB RESULTS
The overall score for Graham Creek indicates a poor condition for Mud crabs in this zone. Since 2018, Graham Creek has consistently received a poor grade (D). Abundance and sex ratio scores remained very low, similar to the previous year, indicating low catch rates and poor balance between male and female crabs. A high score (0.73) for prevalence of rust lesions indicates a low incidence of this condition at Graham Creek, however this score reflects a decline in grade for this zone from very good (A) in 2023 to good (B) in 2024.