Water level fluctuations, a naturally occurring phenomena in the Great Lakes, cause a continuing rejuvenation of lake-influenced wetlands. Two Lake Ontario wetlands (Campbell and Sage Creek Marshes) were mapped for 1 ft. contour intervals and habitat-vegetation type. Historical habitat/vegetation conditions were evaluated through interpretation of aerial photography. The photography was selected to represent water levels different from the current. Habitat types defined at Campbell Marsh and their most important herbaceous species include: (1) narrow-leaved persistent emergents,Typha glauca; (2) aquatic bed,Ceratophyllum demersum; (3) grass sedge,Calamagrostis canadensis; (4) scrub/shrub,Cornusspp; and (5) flooded deciduous forest,Fraxinusspp. Habitat types defined at Sage Creek Marsh and their most important herbaceous species include: (1) narrow-leaved nonpersistent emergent,Sparganium eurycarpum; (2) broad-leaved nonpersistent emergent,Pontederia cordata; (3) aquatic bed,Elodea canadensisand (4) grass sedge,Calamagrostis canadensis. Computerized data analysis showed that vegetation types occured within rather distinctive elevational ranges. As water levels changed, the area of the various habitat types changed, adjusting to both the new water depth and to the size of the area at that depth. In Sage Creek Marsh a large area of narrow-leaved nonpersistent emergents was lost as water levels increased. The greatest loss in Campbell Marsh occurred to persistent emergents; however, this loss did not have a linear relationship to annual mean water depth.