Time-of-Flight (ToF) cameras underwater is used for estimating position, number, depth, shape, size or mass of freely movable object, particularly underwater such as fish. The apparatus comprises a modulated electromagnetic (EM) radiation source configured to illuminate an object of interest and a 3D Time-of-Flight (ToF) camera comprising a matrix of pixels. The matrix of pixels is configured to gather reflected modulated EM radiation and a controller is configured to determine depth information from phase information of reflected EM radiation gathered by the matrix of pixels. The modulating EM radiation source comprises at least one wavelength component with a wavelength lower than that of visible red light. Also provide is similar apparatus in which the modulated radiation source is configured to emit sufficiently high intensity of radiation so that phase information relating to distance information is extractable in reflected radiation received by the camera.
