We present a study of the spatial and redshift distributions of Sloan Digital Sky Survey (SDSS) galaxies toward the position of CrB-H, a very deep and extended decrement in the Cosmic Microwave Background (CMB), located within the Corona Borealis supercluster (CrB-SC). It was found in a survey with the Very Small Array (VSA) interferometer at 33 GHz, with a peak negative brightness temperature of -230 muK, and deviates 4.4-sigma from the Gaussian CMB (G\'enova-Santos et al.). Observations with the Millimeter and Infrared Testa Grigia Observatory (MITO) suggested that 25$^+21_-18% of this decrement may be caused by the thermal Sunyaev-Zel'dovich (tSZ) effect (Battistelli et al.). Here we investigate whether the galaxy distribution could be tracing either a previously unnoticed galaxy cluster or a Warm/Hot Intergalactic Medium (WHIM) filament that could build up this tSZ effect. We find that the projected density of galaxies outside Abell clusters and with redshifts 0.05Comment: 11 pages, 5 figures, 3 tables. Accepted in MNRAS