Many fish species undertake migrations as part of their basic behavior. In addition to the long migratory routes, many species of fish and other aquatic organisms migrate in the medium and short distances, especially from one part of the watercourse to the other. Migration can take place due to various reasons and factors in certain phases of life cycle of aquatic organisms. People have started to interrupt the longitudinal connectivity of watercourses by building barriers and dams for their own needs and so destroyed many centuries of migratory habits of aquatic organisms. The aim of the construction of fish passes is to mitigate the consequences of the building dams and barriers to achieve free passes for all aquatic organisms in rivers and streams. However It should be noted that every construction of a properly functioning fish passes is always just a second-best solution and does not replace natural connectivity. Fish passes are therefore structures that facilitate upstream and downstream migration of aquatic organisms over obstacles and barriers. Fish passes can be designed as technical fish passes, which are more artificial types or close-to-nature types. Both types of fish passes try to create the best possible imitation of natural conditions that are specific for watercourse in a particular area
