In shallow water areas of open Lake Baikal, filamentous green alga of the genus Spirogyra grows abundantly. Together with alga of the genus Ulothrix, it forms algal mats. According to our observations from 2010 to 2013, the spawning habitat conditions for the yellowfin sculpin Cottocomephorus grewingkii (Dybowski, 1874) (Cottidae) proved to be significantly disturbed in the littoral zone of Listvennichnyi Bay (southern Baikal), which, in turn, reduced the number of egg layings. With a 100% projective cover of the floor and a high density of green filamentous algae, the shallow-water stony substrate becomes completely inaccessible for spawning of the August population.