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The Fish Ladder: A helping hand for native fish

Following many years of negotiation between government departments and catchment management committees a fishway or fish ladder was installed on the Lane Cove River to give the local native fish a helping hand. Anyone heard of a fishway or a fish ladder? Some say they are a supermarket for wading birds and other fish eating predators. Others say they are essential to native fish where a river has been blocked.

The river has a weir constructed across it that effectively dams the river, preventing the normal migration of native fish both upstream and downstream. The original weir was constructed in 1938 to create a freshwater lake in one of Sydney's most popular picnic spots. Since that time it has served this purpose well with many people having fond memories of swimming and boating in the pleasant bushland surroundings of Lane Cove National Park. But along came development and pollution of the catchment and now the water is so polluted that the National Parks and Wildlife Service advise visitors not swim in the water.

So what use is the weir now?
It is a structure that will cost a lot of money to destroy and a lot of money to maintain in the future. It has many leaks that are getting bigger and the next major flood may knock it over or it may last for another 20 years. One thing is for sure - while it is there, the normal life cycle of our native fish is being interrupted. They are unable to complete their normal migratory breeding pattern of moving upstream from salt water to fresh water in spring and vice versa in Autumn.

The fishway provides the necessary link between salt and fresh water to enable native migratory fish to complete their lifecycle. It is a rock ramp structure that is built into the existing weir. It contains a number of small weirs that allow native fish to work their way back upstream around the existing weir on the river. So why build a fishway into a structure that is falling down? Basically, the native aquatic critters have had enough. It has been known for a long time that the native bass and other species that live in the river have been suffering as a result of the weir. At times National Parks staff have been known to give the native fish a helping hand by catching the bass hanging around below the weir in a net and letting them go in the freshwater so they can swim upstream. Now the fishway will enable the fish to do it themselves.

Unlike Northern Hemisphere fish such as salmon that can leap tall waterfalls with a single leap, our natives are rather lazy and prefer to flip-flop their way up creeks and streams. The Lane Cove River fishway is designed to allow for this type of behaviour, providing plenty of pools along the way so the fish can catch their breath. Now they only need to escape the watchful eye of the white faced heron that has installed himself in the fishway.

Written by Lee de Gail, former NPWS Ranger at the park

Addendum

Until early 2009, operation of the fish way was limited to the top of the tidal cycle when water overtops the culvert at the downstream end.

A new section below the weir allows fish to access the 'ladder' provided there is enough water depth along its length to cover the grouted edges and constructed rock pools. This will now be during most of the tidal cycle.

A wooden boom has been installed at the upstream end of the fish ladder diverts large woody debris and other rubbish away from the fish way exit.

Top of page


The fish ladder soon after construction


Revegetation has taken place and a White-faced Heron has taken up residence at the narrow end of one of the larger pools


It's a great spot - the fish have to swim right past!


The new section downstream of the weir

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