First report on PST producing benthic cyanobacteria in Lake Baikal is presented.

Cyanobacterial bloom was detected on diverse substrates, including endemic sponges.

Microscopic examination found that Tolypothrix distorta dominated in the fouling.

PCR and sequencing detected sxtA gene involved in saxitoxin biosynthesis.

Eight PST variants were identified using a MALDI mass spectrometer.