ENVIRONMENTAL
RESULTS
ABOUT THE ZONE
South Trees Inlet is a mangrove and salt pan-lined tidal inlet that flows into the Mid Harbour Zone.
WATER & SEDIMENT
South Trees Inlet received an overall water quality score of 0.79 (B).
Sediment quality of South Trees Inlet was very good with an overall score of 0.97 (A).
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The following graphs compare the Water and Sediment scores reported for 2025 (top line) to those from 2024.
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 South Trees Inlet scored 0.79 and received a Good (B) grade, similar to the 2024 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 chlorophyll-a, and dissolved metals – aluminium, copper, lead, manganese, nickel and zinc).
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South Trees Inlet received a Very Good (A) grade for pH (1.00), a Good (B) grade for turbidity (0.68), and Satisfactory (C) grades for total nitrogen (0.51) and total phosphorus (0.62). All of the six of the dissolved metals received a Very Good (A) grade, indicating that average concentrations for these measures were within the guideline values for this zone. Chlorophyll-a received a Poor (D) grade.
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For Sediment quality, South Trees Inlet received an overall score of 0.97 and a Very Good grade (A), 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). The results reflect that all concentrations were below the guideline values for this zone.
HABITATS
SEAGRASS (MEADOW 60)
This zone has one long-term monitoring meadow which sits off the northern tip of South Trees Island. Meadow 60 is an intertidal meadow and the second smallest of the 14 monitored meadows. The meadow improved a grade from Good (B) in 2024 to Very Good (A) in 2025, due to an increase in biomass (2024: 0.81, 2025: 0.88).
MANGROVE RESULTS
The 2025 Gladstone Harbour Report Card incorporates the 2024 Mangroves results. Mangrove condition has historically remained stable due to strong buffering capacity, and since 2019, monitoring has been undertaken every five years. In 2024, the overall grade for Mangroves at South Trees Inlet retained a Satisfactory (C) grade.
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The mangrove extent sub-indicator, which measures changes in canopy cover relative to saltmarsh and saltpan areas, retained a Good (B) grade. The canopy condition indicator, based on remote sensing of canopy density and health, improved from Satisfactory (C) to Good (B). However, shoreline condition, assessed through aerial surveys of mangroves bordering Gladstone Harbour’s water quality zones, declined to Poor (D) in 2024.
FISH & CRABS
FISH RECRUITMENT RESULTS
Fish recruitment was assessed for two species: Yellowfin bream Acanthopagrus australis and Pikey bream A. pacificus. The overall score for 2025 was higher than the previous year (2024: 0.39, 2025; 0.63) and improved from a Poor (D) to a Satisfactory (C) grade. This is a result of increased catch numbers of both Yellowfin (2024: 17, 2025: 62) and Pikey (2024: 23, 2025: 31) bream.