Water
quality
KEY FINDINGS FROM OUR 2024 REPORT CARD
The Ross and Black are Townsville’s two basins, and water quality is monitored in both their freshwater (upstream) and estuarine (downstream) environments.
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Water quality in the Ross Basin receives ‘good’ grades but is declining
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In the 2024 Report Card the Ross Basin receives an overall grade of ‘good’ for water quality in both its freshwater and estuarine environments. This represents a decline from ‘very good’ to ‘good’ in the estuarine environment due to increased levels of nutrients.
Monitoring also shows there are more nutrients in the Ross Basin freshwater environment than found in previous years, particularly in the Bohle River sub-basin.
However, the Bohle sub-basin receives some ‘very poor’ water quality grades
For the fifth Report Card in a row, elevated levels of nutrients have been found in the Bohle River freshwater sub-basin.
The grade for total phosphorus in this sub-basin remains ‘very poor’ and the grade for nitrogen has declined from ‘poor’ to ‘very poor’.
In the Bohle River’s estuarine environment, Louisa Creek receives notable water quality grades: a ‘moderate’ for physical-chemical properties — which measure turbidity and dissolved oxygen — and a ‘poor’ for overall nutrients, comprising of a ‘very poor’ for total phosphorus.
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Despite only covering about 10% of Townsville’s Local Government Area, almost 50% of our population is packed into this sub-basin. This means half of our town is gardening, driving, building, planting, and operating in the Bohle. It bears a significant urban load.
The data behind the Report Card does not identify specific sources of the nutrient pollution, but the Partnership suggests cumulative factors are having an impact. Declining water quality in the Bohle does require investigation.
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Why nutrient levels matter
Balanced levels of nutrients such as nitrogen and phosphorus in waterways are crucial for maintaining ecosystem health. Excessive levels of nutrients, often stemming from agricultural runoff, wastewater discharge, or urban stormwater, can lead to algal blooms, depleting oxygen levels and suffocation of aquatic organisms.
Conversely, insufficient nutrient levels can impede the growth of essential organisms within the food web, leading to imbalances and potential collapse of the ecosystem.
Black Basin grades remain ‘good’ for water quality, with some exceptions
For the fifth year in a row, both freshwater and estuarine environments of the Black Basin retain their overall ‘good’ grades for water quality, with no significant changes seen in nutrient levels or physical-chemical properties at a basin level.
However, there are exceptions in some freshwater creeks. Althaus Creek and Sleeper Log Creek both receive ‘very poor’ grades for turbidity. Althaus Creek shows ongoing issues with total phosphorus, and Ollera Creek receives a ‘very poor’ for low dissolved oxygen.
In the Black’s estuarine environment, Crystal Creek showed improvements in turbidity. Rollingstone Creek receives a ‘poor’ grade for dissolved inorganic nitrogen — the continuation of a trend seen in previous reports.
Further investigation would be required to identify possible causes for these specific grades within the Black Basin.
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Why turbidity matters:
‘Turbidity’ measures suspended particles in waterways, such as sediments (clays and silts), organic matter, and microorganisms, and can affect the way sunlight penetrates water. High turbidity can interfere with the photosynthesis of algae and aquatic plants and can interrupt fish reproduction and migration by smothering spawning beds or affecting water temperature.
In the Dry Tropics, our fine-particle dry soils are a common driver of turbidity in stormwater runoff; especially where there is a lack of established vegetation in the riparian areas along our creeks and rivers.
