We present a study of the spatial and redshift distributions of Sloan Digital Sky Survey (SDSS) galaxies towards 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 -230μK, and deviates 4.4σ from the Gaussian CMB (Génova-Santos et al.). Observations with the Millimeter and Infrared Testa Grigia Observatory (MITO) suggested that 25+21-18 per cent 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 0.05 < z < 0.12 at the position of CrB-H is the highest in the area encompassed by the CrB-SC. Most of these galaxies are located around redshifts z = 0.07 and 0.11, but no clear connection in the form of a filamentary structure is appreciable in between. While the galaxy distribution at z = 0.07 is sparse, we find evidence at z = 0.11 of a galaxy group or a low-mass galaxy cluster. We estimate that this structure could produce a thermal Sunyaev-Zel'dovich (tSZ) effect of ~ -18μK. The remaining VSA signal of ~ -212μK is still a significant 4.1σ deviation from the Gaussian CMB. However, the MITO error bar allows for a larger tSZ effect, which could be produced by galaxy clusters or superclusters beyond the sensitivity of the SDSS. Contributions from other possible secondary anisotropies associated with these structures are also discussed.