In the coastal zone of the oceans, coastal barriers are quite widespread. Within their limits, inlets periodically arise and exist for a certain time, which is of great geological, hydrological, ecological, and navigational significance. Along the coasts where tidal fluctuations predominate, tidal inlets stand out, which are quite well studied in terms of genesis, morpho-, hydro- and litho-dynamics. Inland, semi-isolated marine basins, where tidal fluctuations do not reach a significant amplitude, are called non-tidal seas. Within the coastal barriers of non-tidal seas, channels periodically arise and develop, which are called breaches or prorvas. Breaches are quite often mentioned in the specialized literature along the coasts of non-tidal seas, but they have not been purposefully studied. In this article, we tried to analyze the conditions for the formation of prorvas within non-tidal seas based on many years of research. We have identified four hydrodynamic situations in which breaches are formed. The presented variety of situations allows us to identify and describe four genetic types of prorvas: storm-generated, storm-surge-generated, wind-stress-generated, and river-stress (fluvially induced). The presented article is the first attempt to analyze the genetic characteristics of the breaches.