<p>Underwater optical ranging has attracted growing attention due to its potential for higher accuracy than acoustic-based approaches. Alternative to typical ranging systems using the temporal/frequency information of lightwaves, a ranging scheme that utilizes spatially structured beams for distance retrieval has been demonstrated recently. In this approach, the beams are composed of Bessel-Gaussian modes carrying different orbital angular momentum orders and longitudinal wavenumbers, exhibiting a two-petal-like transverse intensity profile that rotates along the longitudinal propagation direction. This technique has shown relatively accurate ranging performance in scattering media by retrieving the rotation angle of the structured beam, and it operates using only a continuous-wave laser, without the need for high-bandwidth modulation or detection. This paper reviews the background and recent progress in underwater ranging using longitudinally structured beams and provides a perspective on several research topics for the future implementation of this approach.</p>