Mercury content was analysed in black spruce bark and needles and in the epiphytic lichens found growing on trees. The samples were collected in two distinct boreal forests of northeastern Canada (province of Québec). The chosen sites were far from direct industrial mercurcy sources, and were located close to man made lakes of different ages. The objective of the study was to determine the role of atmospheric transport in the mercury contamination of trees growing in close proximity to reservoirs, both old and recently flooded. The lichen samples contained the highest mercury concentrations; 400-800 ng/g. They were several times higher than in the bark and one to two orders of magnitude greater than that found in the needles. The mercury concentrations measured in the lichens were significantly different between the two reservoir sites, whereas those of the needles and bark were not. The mercury concentrations in the black spruce bark sampled near the reservoirs were almost twice as high (,,d30 ng/g) as those measured in the bark of black spruce trees growing near natural lakes (40--70 ng/g). However no differences were found between the mercury concentrations of young needles sampled close to reservoirs and those sampled near natural lakes, suggesting the existince of a relatively low but stable level of mercury in the local atmosphere.