Genetic diversity of T4-like bacteriophages of the family Myoviridae from oligotrophic Lake Baikal was analyzed using major capsid protein gene g23. Sequences of 58 cloned fragments of gene g23 were determined. The obtained nucleotide and deduced amino acid g23 sequences according to results BLAST-analysis had no analogs in the database GenBank. The group of Lake Baikal T4-cyanophages affecting picoplankton cyanobacteria was revealed. UniFrac analysis showed that uncultured T4-like viruses from eutrophic region of Lake Baikal tended to cluster with those from the distant lake of the same trophic status. This fact suggested that the trophic conditions affected the formation of viral populations, particularly of T4-like viruses, in freshwater environments.