Sediment cores from Lake Suigetsu, Japan, reveal the absence of seawater intrusion into the lake caused by the historically documented tsunami of AD1586 (Tensho Tsunami). A high-precision chronology of the cores established by Bayesian modeling radiocarbon determinations enables us to ascertain the precise position of the historical event in the sediment depth. Diatom analysis of the core shows that a diatom assemblage dominated by freshwater taxa persisted through the period. This makes a clear contrast with the core section around AD1664 when the lake was artificially connected to the sea by a channel, and the subsequent intrusion of seawater was clearly recorded in the sediment cores by the occurrence of marine diatom fossils.
