System (100;101;102) for geolocation of an object in water, comprising: • a first device intended to be immersed in, or to float on, water, the first device comprising a light source apt to emit a light beam, • a second device intended to be immersed in, or to float on, water, the second device comprising a camera for taking 2D images and a measuring device arranged to provide an orientation of the camera relative to a main reference frame defined by three orthogonal axes (X, Y, Z), • a processing unit operatively connected to at least the camera, the processing unit being configured to: • determine a vertical distance (Δz) between the first device and the second device based on the depth in the water of both devices, • capture a 2D image of the first device through the camera, • calculate the pixel position in the 2D image of light beam emitted by the light source of the first device, • calculate a position of the first device relative to the main reference frame based on the pixel position of the light beam, the orientation of the camera, a position of the second device relative to the main reference frame and the vertical distance (Δz) or to calculate a position of the second device relative to the main reference frame based on the pixel position of the light beam, the orientation of the camera, a position of the first device relative to the main reference frame and the vertical distance (Δz). • a first device intended to be immersed in, or to float on, water, the first device comprising a light source apt to emit a light beam, • a second device intended to be immersed in, or to float on, water, the second device comprising a camera for taking 2D images and a measuring device arranged to provide an orientation of the camera relative to a main reference frame defined by three orthogonal axes (X, Y, Z), • a processing unit operatively connected to at least the camera, the processing unit being configured to: • determine a vertical distance (Δz) between the first device and the second device based on the depth in the water of both devices, • capture a 2D image of the first device through the camera, • calculate the pixel position in the 2D image of light beam emitted by the light source of the first device, • calculate a position of the first device relative to the main reference frame based on the pixel position of the light beam, the orientation of the camera, a position of the second device relative to the main reference frame and the vertical distance (Δz) or to calculate a position of the second device relative to the main reference frame based on the pixel position of the light beam, the orientation of the camera, a position of the first device relative to the main reference frame and the vertical distance (Δz). • determine a vertical distance (Δz) between the first device and the second device based on the depth in the water of both devices, • capture a 2D image of the first device through the camera, • calculate the pixel position in the 2D image of light beam emitted by the light source of the first device, • calculate a position of the first device relative to the main reference frame based on the pixel position of the light beam, the orientation of the camera, a position of the second device relative to the main reference frame and the vertical distance (Δz) or to calculate a position of the second device relative to the main reference frame based on the pixel position of the light beam, the orientation of the camera, a position of the first device relative to the main reference frame and the vertical distance (Δz).