The Spanish Harbour (Lake Huron, Ontario) and the lower Spanish River are designated as an Area of Concern (AoC) by the International joint Commission. This paleolimnological study was initiated to provide the missing historical data for the past conditions of the AoC for the Spanish Harbour Remedial Action Plan (RAP), which has been developed to restore and protect the water quality of Spanish Harbour. The study has shown that anthropogenic activities in the watershed have changed the water quality considerably. The changes started about 1930 when metal concentrations started to increase in die basin, and reached maximum levels by ca. 1970. Since about 1970, metal concentrations have declined significantly. The recovery is closely associated with the reductions in emissions from the Sudbury smelters since die early 1970s. The timing of the increase in metal contamination and the post-1970 recovery in Spanish Harbour are similar to the geochemical trends seen in many Sudbury lakes. Although metal concentrations have decreased, the area has continued to receive high nutrient inputs from the drainage basin. Based on the fossil diatom and chrysophyte assemblages, nutrient enrichment appears to have increased in the harbour since the mid-1970s.