The physical fundamentals of laser bathymetry based on measuring the halo radius resulting from diffuse scattering of a laser beam at the bottom of a water body and re-incidence of scattered light on the bottom after reflection from the underside of the water surface have been developed. The effect of the light scattering and absorption in water on the image contrast and visibility depth of the halo is theoretically studied. Algorithms for determining the optical properties of water by the measured dependence of the apparent radiance of the bottom on the distance to the point of the laser ray incidence on the bottom are proposed.