Cladophora was monitored at two sites in western Lake Erie during 1979 and 1980 as part of a lake-wide Lake Erie Cladophora Surveillance Program. Two distinctive zones within the littoral region were colonized by the alga, the eulittoral (splash zone) and infralittoral (defined in the present study as the 0.5-4 depth zone). Cladophora of the eulittoral zone became established in May and remained present until late fall. The infralittoral zone Cladophora exhibited a bimodal growth pattern related to the seasonal temperature regime, with growth occurring from April to July and again from September to November. The infralittoral zone supported by the largest share of biomass, which resulted in nuisance accumulations upon the beaches in the island region. Peak biomass was observed from mid-June to early July, obtaining maximum values for the 1979 and 1980 seasons, respectively.