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Irrigation screening can protect native fish and save irrigators time. Without screens, irrigation pumps in our waterways are sucking up native fish so that they become stuck in the pump itself, or in the irrigation channel. Those fish that survive the pump, enter irrigation channels where they are trapped and are unable to get back into natural waterways.  This is a significant problem, as large numbers of fish are being impacted by unscreened pumps and channels and, once lost from the natural waterway, are unable to contribute to breeding populations.

Irrigation channels usually offer little habitat complexity to support fish populations, and are often drained over the winter period. This results in fish dying, or becoming stranded in isolated refuge pools. The refuge pools have intense competition and predation pressures, putting native fish under serious threat.  For example, in June 2020, The Victorian Fisheries Authority rescued 1,207 Murray Cod, 143 Golden Perch, 199 River Blackfish and one Silver Perch from irrigation channels off the Murray River (Reference: Fish Screens Australia).

Typical irrigation channel where fish can get stranded. Photo credit: North Central CMA

Irrigation is essential for Australia’s economy, providing water to our agricultural sector and urban centres. Since 1929, it has been recommended that irrigators install screens to prevent fish and debris from being diverted into irrigation channels (Register News-Pictorial, 1929). Some irrigators have responded to these calls, however, many screens are ineffective, and actually end up blocking the irrigation system.

Debris blocking a fish screen
Debris blocking a screen
Fish blocking an in-line filter
Fish blocking an in-line filter
Fish on a syphon-irrigated plot
Fish on a syphon-irrigated plot

Photos credit: Fish Screens Australia

This is problematic for both irrigators and native fish, as it is time-consuming and arduous for irrigators to constantly unblock their irrigation system and, as the photos show, it is really bad for fish. Ineffective irrigation fish screens causes harm to native fish in three ways:

  1. Entrainment – is when a fish becomes trapped in a water system
  2. Impingement – is where a fish comes into contact with a screen, trash rack or debris at the intake, causing bruising, descaling and other injuries. If impingement is prolonged or occurs at high velocities it causes direct mortality.
  3. Predation – increases because fish are stressed and by providing habitat for fish and bird predator (Blackley, 2003 – PDF download).

What can we do?

A new fish screen technology, that can now be manufactured in Australia, has been developed by Fish Screens Australia, an organisation based at Cohuna, an irrigation town on the Victorian-NSW border. This fish screen prevents fish from entrainment, impingement and predation in diversion pools, rivers and channels. It has minimal impact on water intake, and is self-cleaning to prevent debris build up.

Diagram showing Old vs new cylinder fish screens
Credit: Fish Screens Australia

Fish Screens has developed several types of irrigation screens to suit a variety of waterway conditions.

Cone screen in water
Cone screens are best for shallow water and high amounts of debris, and work with pumps or gravity-fed diversions. Photo credit: Fish Screens Australia
Cylinder screen on bank
Cylinder screens are best for pumps of various sizes and have a cleaning brush around it. Half-cylinder options are also available for shallower water. Photo credit: Fish Screens Australia
Rotating Screens
Rotating screens are good for smaller pumps and the screens rotate, which allows it to be cleaned by brushes or water jets. Photo credit: Fish Screens Australia
Horizontal screening
The horizontal and vertical screening options involve gravity-fed channels. Photo credit: Fish Screens Australia

Next steps

Adoption of this new fish screen technology is a win-win for irrigators and native fish populations, enabling more efficient irrigation and an estimated reduction in loss of native fish by 90% (Freshwater Fisher Newsletter January 2020). Yet many irrigators remain hesitant to implement. A study in 2012, ‘Reducing the perversion of diversion: Applying world-standard fish screening practices to the Murray–Darling Basin’ (Baumgartner and Boys), found that in order to get more irrigators to introduce these new effective fish screens, a mix of legislation and government-funded construction incentives are required. The incentive programs could involve financial aid or less maintenance requirements than older screens.

With the advent of new organisations like Fish Screens Australia able to produce effective irrigation screens, we now need changes to legislation to make fish screens a requirement for all irrigation pumps and channels. In a recent Freshwater Fisher article, the point was made that these legislative changes would ensure that irrigators screen their pumps and channels, significantly reducing the millions of native fish caught in irrigation pumps. With manufacturing of effective screens now underway, we now need our legislative and regulatory frameworks to catch up.

For more information visit Fish Screens Australia.

Kate McKenna
Author

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