The toxic properties of cyanobacteriae of the Shershnevo water storage basin have been studied. Over almost the whole vegetative period of 2005, the cyanobacteriae of the Shershnevo water storage basin may be characterized as high toxic (when intraperitoneally injected to male CBA mice, LD50 was less than 100 mg/kg). There were no interspecific differences between the noninbred animals in cyanotoxin susceptibility. Gender differences were revealed in cyanotoxin susceptibility in CBA and noninbred albino mice: quantitative differences in LD50 (males/females) were 1.34 in CBA mice and 1.3 times in noninbred albino mice. The cyanobacteriae of the Shershnevo water storage basin were found to have an irritating effect on the skin and ocular mucosa. It is suggested that the toxins of Shershnevo water storage basin cyanobacteriae may have a damaging effect on human beings.