MILLIONS of dollars of public money have been spent on building slick bicycle paths along the Yarra River. Now the fish get a turn.
After $2.5 million and two years of construction, Melbourne Water is putting the finishing touches on its dramatic new fishway.
Also known as a fish ladder, it will enable some fish species to swim upstream at Dights Falls, Abbotsford, for the first time in decades.
A two-metre-high weir has blocked migration of freshwater fish to feed and spawn since it was constructed for a flour mill in the early 1840s, save for occasional freak floods.
A 1993 attempt to build a basic fishway out of staggered rocks next to the weir later failed, partly due to low flows from the drought.
David Ryan, Melbourne Water's general manager of waterways, said data had shown that stocks of 11 native migratory freshwater species were dwindling.
These include the Australian grayling, classed as "vulnerable" in conservation terms, which at an average 20 centimetres long, was unable to swim the weir.
Others include the short-finned eel, the Murray cod and the Australian bass.
Mr Ryan said after consultation with community groups, Melbourne Water incorporated a fishway into its $8 million reconstruction of the weir. The prime driver was "improving the health of the river" and boosting native fish numbers. Fish stocks would also be boosted for fishermen.
The public is funding it through household waterways and drainage charges.
Just as bike paths have opened new vistas for cyclists and pedestrians, the fishway means the fish will have access to 2000 kilometres of the upstream Yarra and its tributaries for spawning, food and habitat.
The fishway is an 80-metre-long concrete structure built beside the weir.
When a temporary dam is removed next month, part of the Yarra will flow into the fishway. The torrent will be slowed by the water having to traverse 24 compartments with 30-centimetre-wide entry and exit slots, providing rest points for the fish.
The slope represents a climb of about 10 centimetres for each compartment, a much easier proposition for a small fish than the two-metre-high weir. "It breaks up the flow and creates little eddies for them to rest in and they find their way through," Mr Ryan said.
The fishway will be covered by metal grates to protect against predators, and provided the water is not too murky, the public will be able to peer in.
The first water will flow into the fishway in mid-November and the public will have access to the site in mid-December.
Yarra Riverkeeper Ian Penrose said it was good news.
Watch a time-lapse video of the construction at tinyurl.com/9dn6dra
DIGHTS FALLS FISHWAY
HOW IT WORKS
A diversion channel has been built to stream some of the Yarra River flow before it reaches Dights Falls.
This water flows into a concrete fishway comprising of 24 chambers. Each chamber has slot entrances and exits that slow the water, and each has a gradient that raises the fish 10 centimetres.
The gentler gradient compared with the two-metre weir allows smaller fish to swim upstream and emerge into the Yarra above the falls.
A grate will cover the fishway to protect fish from predators and allow public viewing.