The vertical slot fishway is basically a variation on the pool and weir design. It is also a series of pools, but two baffles are placed at the entrance to each pool, leaving a narrow vertical slot for the fish to pass through. This serves to concentrate the flow of water leaving the pool. However, the water in each of the pools is calm enough to allow the fish to rest. When utilizing this type of fishway, it is important to consider the size of the fish prevalent at the blockage to ensure that they will be able to fit through the slot easily.