Abstract: A system for measuring flow of water in large bodies of water or in small pes in which an acoustic signal is transmitted simultaneously via a radio transmitter-receiver system and a projector-hydrophone acoustic system. The electrical and acoustic signals transmitted are received at two preselected locations which are such that they form a right angle triangle with the point of origin of the signals as the vertex of the triangle. The velocity components of the fluid are measured by comparing the delay in time between the transmission of the electrical signal and the acoustic signal started simultaneously from the point of origin. The velocity of the fluid is then determined from the components of the velocity so determined.