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After 55 years of continual submersion in a subarctic reservoir, the trunks of conifers (Abies balsamea, Picea mariana , and Pinus banksiana ) are little modified and only slight peripheral degradation is visible. The content of NaOH (1%) extractible material and pentosans is slightly decreased, but changes in the level of acid-insoluble lignin and wood density are negligible, indicating that the dense lignous network remains practically unaltered. At the histological level, the woody tissue contains several fungal hyphae and exhibits enlarged bordered pits. These slight modifications presumably result from an additive microbiological action of soft-rot fungi and of certain bacteria. The physico-chemical conditions prevailing in the reservoir permit the development of these decomposers but the relatively low water temperature limits their action.