Intertidal monitoring during 1992 and 1993 at mid to low intertidal rocky-shore beaches surrounding two marine-discharging pulp mills in British Columbia revealed a decline of biodiversity as the sites were closer located near the mill outlet. The present study reports spatial changes in species richness, trophic composition and algal composition of intertidal benthos over a gradient of effluent exposure. Those spatial trends are related to dioxin/furan loads in sediment, Dungeness crab (cancer magister) hepatopancreas and Pacific oyster (Crassostrea gigas) muscle, sampled in the same area but at slightly different locations. Local oceanographic conditions and non-pulp mill pollution sources in the vicinity of the two pulp mills are considered as confounding factors in assessing pulp mill effluent. Statistical analyses were used to assess trends in intertidal biodiversity. A GIS-approach, incorporating the most important known oceanographic features, is a very helpful additional tool to visualise the major relationships between intertidal biodiversity and contaminant loadings. This study has discovered that in some regions cumulative contamination may exert a large and long-lasting effect on intertidal diversity and community structure even when current pollution has decreased. Feeding guilds deemed very useful tools to reflect shifts in the functioning of a given area. Deposit feeders were highly abundant on isolated patches close to the mill with abundant sources of organic material. Green algae deemed tolerant to pulp mill effluent whereas red algae were the most sensitive to bleached kraft pulp mill effluent. This study suggests that environmental impact is not always proportional to the volume of pulp and paper production and waste loading but highly depends on local oceanographic conditions and historic depositions. There is a strong need for long-term monitoring to complete the accurate assessment or potential sublethal and ecosystem effects, and to understand the bioaccumulation dynamics of effluents on a site-specific basis. In the summer of 2004, intertidal monitoring will be repeated at the same sites, which aims to detect long-term changes in biodiversity and to evaluate the impact of historic contaminated sediment deposits. This paper serves as a preliminary study to propose a sampling regime and recommend appropriate analysis for interpreting the results.