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Fish lock or fish lift - A fish lock is built into a dam. It consists of two chambers, one at the bottom of the dam and one at the top, which are connected by a vertical or sloping shaft. There is a movable gate, or sluice, between the upper chamber and the reservoir that can be opened and closed. Similarly, there is a sluice between the lower chamber and the river. To allow the fish pass upstream, the sluice to the upper chamber is closed, while the sluice to the lower chamber is left open so that the fish can enter it. Every few hours, the lower sluice is closed trapping the fish in the lower chamber. The upper sluice is then opened and the shaft and upper chamber fill slowly with water. The fish are raised through the height of the dam and they swim out into the reservoir through the top chamber. The lock is operated in reverse to allow the fish to pass back downstream.
Cross-section of fish lock