Measurements of density flow (m3 / s / m) or equivalently current velocity, due to astronomical tide have been made, with different current-meters not only in the entrance but also along the estuary in its more narrow part between Punta San Carlos y Punta del Vispón. These measurements have been taken so well in the surface level as in depth. The used numerical model solves equations, depth averaged, of continuity and conservation of momentum with a method of finite differences and the numerical simulation has run with a length of two tide cycles, each one of about 12h 15 min. Comparison between real and calculated values, in terms of maximum modulus of current velocity can be considered acceptable. The advantage of using a numerical model is that values of the unknowns (surface elevation and the two components of the velocity vector) are determined in all the points of the set grid of the modulated area, with a grid space of 20 m.