Fossiliferous sediments have long been known to occur along the banks of the Goulais River. Radiocarbon dating has established their time of deposition as late in the Nipissing transgression. Sedimentary environments and fluvial conditions in the ancestral river channel shaped fossil assemblages. Pollen reflects regional upland forests of Pinus and Picea, with other trees and shrubs such as Quercus, Fraxinus, Acer, Ulmus, and Alnus. Forested peatlands, fens, and emergent and submerged aquatic communities were common in lowland valleys and along the floodplain of the river. These reconstructions are supported by aquatic insect fossils and hygrophilous taxa such as Micropeplus sculptus and Elaphrus olivaceus and also are confirmed by plant macrofossils such as Myrica gale, Triadenum virginicum, Dulichium arundinaceum, Typha, Brasenia schreberi, Potamogeton spirillus, and possibly Zizania palustris. There is no evidence for regional climatic change during this portion of Holocene time.