We present the results of the one year monitoring of absorption and scattering lengths of light with wavelength 375–532 nm within the effective volume of the deep underwater neutrino telescope Baikal-GVD, which were measured by a device «BAIKAL-5D». The «BAIKAL-5D» was installed during the 2020 winter expedition at a depth of 1250 m. To carry out the optical measurements, we use a device with a shaded point-like isotropic light source having a spectral resolution of about 3 nm. A wide angle light receiver is moved by a stepper motor so that the distance between the receiver and the light source can vary from 0.9 m to 7.4 m. The absorption and scattering lengths were measured every week in 6 spectral points. The short-time variation of absorption length was estimated.