Water for native fish: Mehi River flow

Water for the environment is being delivered to the Mehi River to replenish refuge pools for native fish and to provide a low flow connection event along the entire length of the Mehi River to support a healthy river system.

Murray cod (Maccullochella peelii)

About the site

The Mehi River is approximately 315 kilometres long, located in the Gwydir valley floodplain downstream of Moree in north west NSW. The Mehi River is home to a variety of native plant communities including river red gum, coolibah and black box riparian woodlands and it provides important refuge sites for native fish such as Murray cod, golden perch and eel-tailed catfish.

Very dry conditions and record high temperatures have persisted across the northern basin over the last two years, with low rainfall and very high evaporation rates.

The upper and central reaches of the Mehi River have not flowed since the completion of irrigation and water for the environment deliveries in mid-February 2019. These reaches have dried down to a series of pools which are gradually falling to lower levels.

The lower reach of the Mehi River (downstream of Ballin Boora Creek) has experienced extended drying since the Northern Connectivity event finished in June 2018. Since last June the Mehi River at Bronte has experienced only 11 days of very low flow and 294 days of no flow. The Mehi River near Collarenebri has had 28 days of low flow and 235 days of no flow.

Fish in the now isolated and drying waterholes in the lower Mehi reach are showing signs of stress due to reduced food sources, over-crowding, and poor water quality. While fish and pools in the upper and central Mehi River sections remain in a good to moderate (upper) to fair condition (central) it is preferable to provide a flow and refresh these pools before native fish become stressed, water quality declines and water levels drop further.

Aims of this watering event

This watering event aims to refill refuge pools in the Mehi River to support the survival of native fish and provide a low connectivity flow along the entire Mehi River system.

In addition, this delivery of water for the environment will support the many Aboriginal environmental, cultural and spiritual values that are present in and along the Mehi River system. The flows will also have many community benefits including supporting recreational uses and helping support water supplies for households and livestock.

Specific objectives

Fish: Help native fish including Murray cod and eel-tailed catfish to survive the dry conditions.

Habitat and connectivity: Improve river connectivity and habitat for native fish and animals.

Supporting objectives:

  • Riparian vegetation and plant communities: Improve riparian vegetation condition and maintaining extent.
  • Other dependent fauna: Provide resources and refuge for other native fauna.
  • Aboriginal Values: Support Aboriginal cultural, environmental and spiritual values.
  • Social/Human: Support domestic and livestock, and human recreational needs.

Sources of water

3,700 megalitres of Commonwealth water for the environment and NSW Environmental Contingency Allowance (ECA) will be delivered from Copeton Dam.

Hydrograph and water delivery details

Hydrograph showing the flow rate being delivered to the Mehi River

Hydrograph showing the flow rate being delivered to the Mehi River

Delivery dates

Releases commenced 15 April from Copeton Dam. The flow rate will remain low ranging from 50 to 200 megalitres per day to maximise the outcomes.

Monitoring for this Event

Flow: The flow will be monitored using the gauge network and satellite tracking. Flow will be monitored by river operators, compliance officers and environmental water managers.

Water quality: Monitoring undertaken by Eco Logical Australia, NSW DoI – Water and WaterNSW will provide water quality information during the flow.

Fish: NSW DPI – Fisheries is undertaking long-term monitoring of fish populations in the northern rivers as part of the Basin Plan Environmental Outcomes Monitoring.

Fish movement: As part of an existing project, Department of Industries – Water and DPI – Fisheries installed equipment (an acoustic array) to monitor movement of tagged fish in the Mehi, Macintyre River and Barwon Rivers. This array may record the movement of tagged golden perch during the flow.

Who decides where and when water will be delivered

The Mehi River Flow has the support of the community-based Gwydir Environmental Water Advisory Group which recognises the need to balance current and future environmental needs within the Gwydir catchment with the immediate needs of native fish and animals in the Gwydir and downstream catchments (Barwon).

The NSW Government is partnering with the Commonwealth Environmental Water Office to deliver the Mehi River Fish Flow. Other agencies that will contribute include NSW DPI – Fisheries, DoI – Water, WaterNSW and the NSW Natural Resource Access Regulator. This is an example of government agencies working together to deliver outcomes under the Basin Plan.

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