Pesticide runoff from farms into local waterways has dropped, particularly in the southern Wet Tropics region, a new report into waterway health has revealed.

Wet Tropics Waterways Chair, Dr Greg Vinall, said the latest Wet Tropics Waterway Health Report Card reveals that most freshwater rivers and estuaries from the Daintree to Ingham’s Herbert River continue to be in ‘good’ or ‘very good’ condition. However the standout result is a recent drop in pesticide detection levels in several Wet Tropics catchments.

“After several years of increases – which spiked between 2016-2018 – there is now clear evidence of a downward trend,” he said. “This is particularly true for the pesticide chemical called imidacloprid which is highly soluble and mobile, with a high risk of ending up in waterways where it is detrimental for aquatic bugs and crustaceans.”

Dr Vinall said the turnaround was a direct result of positive action taken by the agricultural industry to reverse the trend.

Imidacloprid is an insecticide used by the agricultural industry to control outbreaks of cane grub, a beetle that feeds on sugar cane roots, causing the plant to die.

Greg Shannon, Cane Productivity and Development Manager at Tully Sugar, said imidacloprid is invaluable to cane growers.

“Imidacloprid is currently the only solution available for controlling cane grub outbreaks, so it is essential that the industry keeps its social licence to use it,” he said.

“As detections of imidacloprid were increasing, we got together with industry partners to deliver a program to raise grower awareness. There was very strong buy-in from growers because using less imidacloprid is a win-win.

“Growers are also dealing with a soil disease, Pachymetra, which has similar symptoms to a cane grub outbreak. Sugar cane varieties have been developed, and successfully trialled, that are resistant to the soil disease and that’s helped growers to use imidacloprid more strategically. Growers have also been modifying equipment to improve insecticide placement depth and soil coverage, further reducing losses to the environment.”

As a result, less than five per cent of water samples collected in the 2019-20 wet season in the Tully catchment exceeded imidacloprid guidelines– compared to about 30 per cent in 2016-2017. Since then, the pesticide toxicity risk of imidacloprid in 2021-22 has declined, in the Tully and other catchments, to the lowest recorded level since monitoring began in 2016.

The annual Wet Tropics Waterway Health Report Card assesses the region’s nine catchments and eight estuaries, as well as the inshore marine and offshore marine zones, by analysing and integrating scientific monitoring data contributed by a number of organisations.

Produced annually by Wet Tropics Waterways Partnership, the report card is an initiative under the Reef 2050 Water Quality Improvement Plan, an Australian and Queensland Government framework to improve the quality of water flowing to the Great Barrier Reef lagoon.

The report card is also building a more comprehensive picture of fish barriers in the region.

“Fish populations and diversity are an important indicator of waterway health,’’ Dr Vinall said. “However, there are thousands of fish barriers in the Wet Tropics, such as causeways, weirs and culverts, that stop fish moving between freshwater and estuary habitats to complete their life cycles.

“A study just completed by Terrain NRM has prioritised 200 fish barriers in the Daintree, Dickson Inlet and Barron estuaries that need remediating to improve fish passage between different environments. The next step is to identify funding opportunities to start fixing them so we can increase fish movement and improve fish stocks for both commercial and recreational fishers.”

Minister for the Environment and the Great Barrier Reef, Leanne Linard, commended the Partnership on the release of its 2023 Report Card.

“It’s wonderful to see the collaboration across government, industry and community, working together to better understand and protect the health of local waterways,” Ms Linard said.

“Healthy waterways deliver many benefits for the local community and are vital to the health of the Great Barrier Reef. That’s why the Palaszczuk Government is providing $1.25 million for Reef Regional Waterway Partnerships this year, part of a $3.75 million commitment over three years.”

The Wet Tropics Waterways Partnership is supported by the Queensland and Australian governments, local councils, industry, community and other partners including the host of the partnership, Terrain NRM.