this study takes place in an endangered peatland within the city of thunder bay ontario. the study area, william bog, is one of a few remaining peatlands in the thunder bay district which have developed on abandoned minong phase lake basins on the north shore of lake superior. an inventory of vascular plants, mosses, hepatics, and ground lichens reveals that the vascular flora is richer than the moss or hepatic flora and that ground lichens are rare. vegetation zones identified in the study area are similar to communities described for peatlands in ontario by jeglum et.al. (1974). the study area is centered on a carex spp. dominated graminoid fen which is bounded to the north and west by a conifer swamp, and to the east by a shrub rich treed bog. ordination of vegetation data reveals that vegetation varies continuously from fen to swamp and from fen to bog. the nature and flow of groundwater is related to vegetation type such that within the fen, and to the north and west, vegetation can be classified as mlnerotrophic. east of the fen vegetation appears to be ombrotrophic in nature. the ph of both soil and water, calcium concentration , and conductance of water samples varies continuously along the vegetation gradients. this results in a corresponding environmental gradient which runs from strongly minerotrophic (fen) to weakly minerotrophic (conifer swamp) to the north and west, and from strongly minerotrophic (fen) to ombrotrophic (bog) in the east. william bog exibits consistently higher and lower air temperatures when compared to the thunder bay airport, 3 km sw, this peatland has a significantly shorter frost free period. within the study area peats are coolest in ombrotrophic sphagnum spp. hummocks east of the fen, and frost persists within these hummocks well into the growing season. west of the fen peats are warmer, likely the result of subsurface groundwater flow. there is no evidence of permafrost in the study area. the historical and evolutionary development of william bog is based upon the lateral expansion of phragmites communis marshes through paludification of the sandy lowland basin. this resulted in two developmental sequences which are based upon the flow of groundwater within the basin. minerotrophic communities evolve where groundwater flow is concentrated. ombrotrophic communities develop in drier sites where sphagnum spp. growth elevates the surface above the influence of groundwater. dynamics between these communities are based upon local climatic variations during the period following initial colonization of the site, and disturbance by wildlife. the proposed development of vegetation in william bog appears to resemble sequences proposed by several peatland studies undertaken in northern minnesota, southern ontario, and southern quebec.