Updated 14 March 2023
Seqwater is currently working with project partner BMD Constructions to deliver a new, more flood resilient vehicle bridge across the Brisbane River at Mount Crosby. Once complete, the Mount Crosby Vehicle Bridge will become a new crossing for road traffic to replace the existing Mount Crosby Weir Bridge.
As part of these works, and in accordance with the General Fisheries Permit issued by the Department of Agriculture and Fisheries (DAF) for this project, a number of measures are in place to mitigate construction impacts on the surrounding environment, including:
- Specialist aquatic ecologists onsite to ensure works are in-line with industry best practice.
- An Seqwater environmental representative is also onsite to ensure works are in-line with required works permits.
- Daily water quality testing including dissolved oxygen and temperature tests within the water.
- Instream sediment controls have been deployed.
- Water pumps installed promote water movement over and around the weir. This movement supports downstream aquatic environment.
Water oxygenating through pumps and water quality testing has occurred prior to this event and is continuing to be undertaken at the site. We’re working closely with the Department of Environment and Science (DES) to ensure all practicable steps are taken to manage any possible impacts construction works may have.
Specialist aquatic ecologists are onsite during construction hours assisting with the safe relocation of aquatic wildlife from the worksite area to nearby upstream locations of the Brisbane River.
As at 9 March, more than 13,000 aquatic wildlife had been safely relocated upstream since 20 January. In line with biosecurity procedures, a total of 856 declared pest fish species including carp, tilapia and gambusia have been removed from the river as part of this process.
The project team is aware of a number of fish deaths downstream of the Mount Crosby Weir. Approximately 2,203 dead fish, mostly bass, have been observed. Many environmental factors can contribute to fish deaths in the river.
The Department of Environment and Science (DES) has undertaken an extensive investigation and has found elevated water temperatures as the cause of the fish deaths.
DES noted Australian bass (Macquaria novemacuelata) are the predominant species represented in the fish deaths and is one of the least heat tolerant species of all local fish.
It was also found that the February 2022 floods resulted in scouring of all water plants in this part of the river, which are vital in reducing water temperature by providing shade and creating temperature gradients with depth.
Weather throughout January and February has resulted in overall water temperatures in the Brisbane River in 2023 being some of the highest on record. DES concluded that lack of water plants coupled with the hot weather resulted in the impacts to the most temperature affected species of fish.
Seqwater is committed to continuing to work with the relevant agencies to ensure all appropriate environmental conditions are monitored and where required, appropriate mitigation measures are kept in place.