Swr~.mury:Lmd is a relatively minor element of the eart,h's crust but widely distributed in low concentrations in uncontaminated sediment.ary rocks and soils. The average content of lead on soil is about 10 nigikg; the background levels of lea,d in freshwaters and freshwater sediments are est,imated t o be below 3 pg/l and 40 pg/g, respect'ively. Lead is commonly found in water plant tissues but its essentiality has never been proved. The present paper is aimed a t summarizing literature dnta concerning occurrence of lmd in water environments and its t0xicit.y and bio~tccumrilation mit,h respect, to algae and cyanobacteria. The dat,a concerning mode of toxic action of lead, factors affecting toxicitmy and accumulation, concentration factors of lead in algae and eyanobacteria and lead content. in va.rious algal and cyanobact,eria.n species are given.