A fishway is a
construct that allows undesirable
fish to be blocked from a
waterway. Unlike a
fish ladder, which is designed to increase fish
mobility, a fishway always requires human supervision.
To construct a fishway, you first need an controlled point of entry to the waterway. You must create a bottleneck that forces undesirable fish to use a single pathway to enter. Two "cages" are placed at this point, which allow fish to swim in from one direction, but no allow them to exit. These cages are then pulled up with a crane once or twice a day, and the fish are placed in a tank and then sorted. A sorting table with a smooth ramps leading to either side of the divide.
I am aware of only one fishway, located in the waterway between Cootes Paradise (a very large pond) and Burlington Bay (part of Lake Ontario). It is used to block the entry of carp from the pond, where the number had grown to 50,000 fish, and the entire pond had become a mud-puddle, and native species near extirpation.
The process was incredibly time consuming, with over a hundred carp passing through a day. The program was combined with a fish research program to offset the cost.
There are reportedly several other fishways in existence, including the Maribyrnong River in Melbourne, which has two.