Twentyfive cyanobacterial blooms in Lake Ladoga and adjacent water bod
ies were studied in the summer of 1990-1992. Toxicity of the water blo
om material for mice was detected in 9 cases. The maximal tolerable do
ses (MTD) of the material extracted from biomass varied within 3-30 mg
kg(-1) mouse body weight; 50% lethal doses (LD(50)) were within 45-12
5 mg kg(-1). Toxic water blooms were registered in Karelian lakes and
in the Neva Bay, Gulf of Finland. Cyanobacterial samples collected on
the eastern coast of Lake Ladoga proved to be non-toxic. The species i
dentified in toxic bloom material included Anabaena circinalis, A. flo
s-aquae, A. lemmermannii, Anabaena sp., Aphanizomenon flos-aquae, Gloe
otrichia echinulata, G. pisum, Microcystis aeruginosa and Oscillatoria
sp. These data suggest that toxic forms of cyanobacteria are widespre
ad in Karelian lakes belonging to the drainage basin of Lake Ladoga.