Serological detection of some pathogens in the beluga whale Delphinapterus leucas population from Sakhalinsky Bay of the Sea of Okhotsk (Sakhalin-Amur beluga whale stock) was performed in 2013-2014 after the largest recorded flood of the Amur River (among observations since 1896). The percent of this population that is immune to the causative agents of clonorchosis was 25.6%; toxoplasmosis, 11.5%; brucellosis, 38.5%; tuberculosis, 30.8%; cetacean morbillivirus infection, 16.7%; and to alpha and gamma herpes viruses each, 21.8%.