Pool and orifice fish ladder is almost similar to pool and weir fish ladder and the only difference, in this case, is the overflowing weir is provided with a submerged orifice within its body.
Hence, in this case, the fish can travel to upstream by just passing through each orifice rather than jumping over the weir crest.
Similar to a pool-and-weir system, except that each "dam" has a narrow slot in it near the channel wall.
In this case, the weirs are replaced by walls with vertical slots so that the fish can pass though these slots from pool to pool and to the upstream easily.
Vertical-slot fish passages also tend to handle reasonably well the seasonal fluctuation in water levels on each side of the barrier.
This type of fish ladder is recommended where there is a huge amount of fish migration in the river.
Recent studies suggest that navigation locks have a potential to be operated as vertical slot fishways to provide increased access for a range of biota, including poor swimmers.
Baffle fishway is another type of fishway which is in the form of a rectangular channel with a series of equally spaced baffles perpendicular to the direction of flow.
Uses a series of symmetrical close-spaced baffles in a channel to redirect the flow of water, allowing fish to swim around the barrier.
Baffle fishways need not have resting areas, although pools can be included to provide a resting area or to reduce the velocity of the flow.
Such fishways can be built with switchbacks to minimize the space needed for their construction.
Baffler fishways are of different types, namely:
Denil Fishway
Larinier Fishway
Alaskan Fish Pass
Chevron Fishway
Baffles come in a variety of designs. The original design for a Denil fishway was developed in 1909 by a Belgian scientist, G. Denil; it has since been adjusted and adapted in many ways.
The Alaskan Steeppass, for example, is a modular prefabricated Denil-fishway variant originally designed for remote areas of Alaska.
Baffles have been installed by Project Maitai in several waterways in Nelson, New Zealand, to improve fish passage as part of general environmental restoration..
Rockramp fishways are built using large size rocks andtimber logs.
In this type of fishway, a rock ramp is prepared directly over the obstruction across its width with some slope.
Pools and falls are created by these large rocks in such a way that the fishes can easily pass over them.
Rock ramp fishways are well suitable for low height obstructions, where upstream water level control is not essential and some barriers suitable for rock ramp fishway are low height weirs, short waterfalls, channel stabilization structures, etc.
Uses large rocks and timbers to create pools and small falls that mimic natural structures.
In this type of fishway, a rock ramp is prepared directly over the obstruction across its width with some slope.
Fish elevators also called fish lift is another type of fish in which the fish is lifted from the bottom to the top by a chamber filled with water.
Breaks with the ladder design by providing a sort of elevator to carry fish over a barrier. It is well suited to tall barriers.
Compared to ladder-type fish passes, the fish elevator facilitates a huge amount of fish migration at a given time.
Some larger-sized species cannot travel upstream nearby due to smaller size openings, poor swimming capabilities.
For such type of species, Fish elevators are best suitable.
Fish lifts are well suitable for tall obstructions such as arch dams, high weirs, etc.
When enough fish accumulate in the collection area, they are nudged into a hopper that carries them into a flume that empties into the river above the barrier.
On the Connecticut River, for example, two fish elevators lift up to 500 fish at a time, 52 feet (15.85 m), to clear the Holyoke Dam. In 2013, the elevator carried over 400,000 fish.