Abstract: Swimming pool basin provided with a partition wall, which can be moved essentially vertically up and down, for the division of the swimming pool basin into part-basins, the partition wall comprising an oblong, essentially beam-shaped body, which extends between two mutually opposing, vertical walls of the swimming pool basin, and which partition wall can be brought into a first, operative state so as to lie with its upper limit essentially level with the water level or project above it, in which first state the swimming pool basin is sub-divided into two swimming sections, and into a second or retracted state, in which the upper limit of the partition wall is located at a good distance below the water level, enabling swimmers to swim unhindered past the partition wall along the top, the oblong body of the partition wall being directly attached by means of at least two movable guide arms to the swimming pool bottom or to a wall part of a recess made in the swimming pool bottom.