Annual fish monitoring data for 20 lakes across Canada. Collection season was standardized to provide temporal comparability within each lake. In most lakes, fishing occurred in the fall. Predator fish were limited to trout, pike or walleye, to facilitate spatial comparisons. Ten to twenty top predator fish were targeted per lake. In cases where population/conservation concerns existed, only ten fish were taken. Prey fish were also collected; ten to twenty individuals of a single species that the top predator was known to eat. A range of fish sizes were targeted wherever possible. Physical parameters recorded include species, length, weight, age and sex. Predator fish (fillet and/or whole body samples) and prey fish (whole body samples only) were analysed for mercury, metals, and stable isotopes.