The effects of dimensionless parameters and boundary friction on air-entraining vortices and the critical submergence of an intake located in no-circulation imposed cross-flow and still water are investigated. It is found that limit values affect these vortices and the critical submergence, depending on the flow and geometrical conditions. The slower the cross-flow is, the higher these limit values are. The boundary friction effects on air-entraining vortices at intakes located in both a cross-flow and still water are also examined. The boundary section close to the free surface has a much larger effect than the boundary section away from it. The frictional effect of a boundary section on an air-entraining vortex depends on the distance between the boundary and the vortex centre at the free surface (above the intake centre). The boundary has maximum frictional effect if it is located at the vortex centre.