Thompson Pond, a bog lake in Pine Plains, New York, has flora indicative of both ombrotrophic and minerotrophic conditions. Distinct community types within this wetland system include a peripheral moat, hummock swamp, floating vegetation mats, peat rafts, aquatic floating-leaved and submergent macrophytes, and open water. A false-bottom of unconsolidated peat overlies the lake bed. Vegetation composition is typically diverse in such lakes, which support species of both acidic and calcareous habitat affinities. We repeated a 1973–74 survey to assess changes in wetland flora after four decades. The recent survey yielded 218 vascular plant species, representing 66 families and 134 genera. The largest genus was Carex with 26 species. Forty species from the original survey were not relocated, and 97 species were found in the recent survey that had not been found in the original survey. Eriocaulon aquaticum, usually associated with oligotrophic waters, was common in the original survey and not found in the recent survey. Aerial photos were used to calculate the change in vegetation cover, revealing that floating vegetation mats and peat rafts expanded between 1970 and 2016. Nutrient loading from agricultural and residential land use within the watershed, in addition to the installation of a dam across the lake’s surface water outlet have likely contributed to the floristic and community structure changes seen in Thompson Pond.