In the recent decades due to the technical river training which used hydrotechnical structures the river’s continuity has been broken. It had a negative impact on the decline in many fish species. Currently, many restoration projects of river beds in Poland are combined with the restitution of anadromous fish were implemented. The success of these programs depend on the restoration of the ecological corridor of the river. A fishway is a structure on or around artificial and natural barriers, such as dams to facilitate fishes natural migration. The most effective fishway is the one close to nature. Hydraulic conditions within it are similar to mountain stream. The downside of this solution is the cost of construction and the large area its occupy. Technical fishways occupy less space but are less effective. A combination of the advantages of both solutions are rock ramp fishway where sequences of pools are made of natural stone. The results of numerical modeling for rock ramp fishway with the main slot located transverse to the bed slope were shown. Within such construction of fishway there are two main directions of flow – transverse by the main slot and the consistent with the bad slope through the smaller slots. The impact of the changed width of the main slots and other slots on the hydraulic condition were calculated.