From sea to river, fish migrate one ladder at a time

Hundreds of thousands of fish each year are anticipated to start moving through a new passage – known as a fish ladder or fishway – opened this week at the Tauwitchere Barrage near Goolwa, designed to improve their migration between the Coorong and Lower Lakes.

Fishways provide a way for native fish to move freely through structures such as weirs, locks and barrages along the River Murray and its tributaries, which would otherwise block their travel for activities such as, breeding and accessing new habitat.

The $250,000 project undertaken by SA Water on behalf of the Murray–Darling Basin Authority, is part of a wider ongoing program of works to construct fishways and allow free migration from the Southern Ocean in South Australia, upstream to Hume Dam near Albury-Wodonga.

SA Water’s Senior Manager of River Murray Operations Garry Fyfe said early fishways used in parts of France in the 17^th century were made of bundles of branches, which created steps in steep channels to bypass obstructions in local rivers.

“The idea around modern fishways is still pretty much the same, but these days we use mostly precast concrete,” Garry said.

“Each weir or barrage is different, so each fishway needs to be tailor-made. There are a range of different designs, which vary based on factors like local river conditions and the physical characteristics and swimming abilities of fish migrating through the area.

“At Tauwitchere, we’ve installed a trapezoidal fishway that can operate over a wide range of water levels to target the movement of both small and large fish.”

The trapezoidal fishway is comprised of a straight channel divided into a series of interconnected pools, which slows down the flow of the water, making it easier for fish to travel through. The pools include areas of high and low velocity water, which suits the movement of fish of different sizes.

“This is the fourth fishway to be constructed at Tauwitchere Barrage and at only four metres wide and 15 metres long, is relatively small in comparison to the 3.6 kilometre long barrage.”

The new Tauwitchere fishway is the last of six to be constructed as part of the Commonwealth-funded Construction of Fishways Management Action under the Coorong, Lower Lakes and Murray Mouth recovery project.

Fish found to be using the fishways on the Murray barrages include freshwater species like Australian Smelt, Bony Herring and Golden Perch, as well as diadromous species like Congoli, which must move between the ocean and river to complete their lifecycle.

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