Fishways are constructed onto large waterway barriers such as dams, weirs and tidal barriers, to help provide adequate fish movement across the barrier. They are used as a last resort when there is insufficient water flow above or through the barrier to assist fish movement. There are three types that have been successfully used on waterway barriers in Queensland:
- rock ramp fishways
- vertical-slot fishways
The vertical height of the waterway barrier usually dictates the type of fishway required.
Rock ramp fishway
Rock ramp fishways are commonly used for low height barriers to about two metres. They are essentially a ramp of rocks placed immediately below a barrier, creating a low slope that simulates a rocky stream bed. Larger boulders are placed at strategic points along the rock ramp, creating pools of low flow and low turbulence which allow fish to move from pool to pool and over the weir.
Vertical-slot fishways are used for medium-sized weirs up to six metres high. This design generally consists of a concrete channel extending from the top of the weir (headwater) to the base of the weir (tailwater). Concrete walls or baffles are then inserted along the length of the channel to slow the velocity of the water.
Fishlocks are used to transfer fish over high dams which are typically over 8-10 metres tall. Fishlocks consists of a forebay chamber at the tailwater (base of the weir) connected to a vertical chamber which extends to the top of the weir. There is an exit chamber at the top of the vertical chamber. When water is discharged from the fishlock, migrating fish are attracted into the forebay and then into a cage at the bottom of the vertical chamber. The vertical chamber is then filled with water and the cage floats to the top, where another attraction flow and a crowding device entice fish to swim into the exit chamber. This chamber then provides a pathway into the impoundment upstream of the weir. The whole process is controlled by an on-site computer.
New innovations in fishways include fish lifts.