Fishway construction and Hymenachne spray

Jun 22, 2016 |

Reef Catchments project to improve fish passage in the Rocky Creek catchmentWhat’s happening at this site? Reef Catchments is working with a landholder to improve fish passage and habitat through waterways in the Rocky Dam Creek Catchment. A partial width rock ramp fishway was constructed on an existing fish barrier adjacent to a large wetland area near Koumala. A Hymenachne infestation in the wetland was also sprayed, to improve the water storage capacity and improve dissolved oxygen levels.

Who’s involved? This is a Reef Catchments project, with co-funding from the landholder and through the Australian Government Reef Programme. It is part of the wider Rocky Dam Basin System Repair program.

Project: Fishway construction and Hymenachne spray: Wetland, Koumala

Project Goals:  To improve fish passage and habitat of important migratory species through the Rocky Dam Basin.

Current Activity: With assistance from the Australian Government Systems Repair funding (Reef Programme), a partial width rock ramp fishway was constructed on a priority barrier, connecting salt and freshwater environments. During flows migratory fish such as Empire Gudgeon, Barramundi, Crescent Perch and Giant Herring are able to move though the fishway. The design has small drops and deep pools to reduce turbulence and provide suitable conditions for movement of juvenile fish and small species.

The wetland is seriously infested with Hymenachne.

This is reducing the water capacity within the wetland and impacting on dissolved oxygen levels. During monitoring in April 2016, dissolved oxygen levels in the wetland were recorded at ~4% for the open water channels. These levels are critical and very little life can be sustained. It has been demonstrated in other wetlands that controlling Hymenachne has improved dissolved oxygen levels within waterways. The control will also have added benefits of increasing the water storage capacity for the landholder. Reef Catchments has funded the aerial spray of 30ha of the Hymenachne, focusing on the old channels and deeper water, which is not suitable for grazing.

Status: The fishway was constructed in late 2015. It was apparent from fishway monitoring in February 2016 that diversity and numbers where lower than in nearby wetlands without major Hymenachne infestations.  In April 2016, 30 ha of Hymenachne was sprayed using a helicopter.

Future plans: Reef Catchments, with approval from the landholder, plans to undertake a second spray of the same area to ensure the suppression of the weed. Follow up monitoring will also be undertaken to compare water quality results, in particular dissolved oxygen levels of the open water. Reef Catchments plans to continue working on the critically important wetland.