More than half of the annual acidic deposition to Canada's boreal forests is released during spring snowmelt. To evaluate the impact of this acidity upon the aquatic environment, the sources and hydrologic pathways must be defined. Two environmental tracers, oxygen 18 and silica, were used to meet this objective for spring snowmelt at Lac Laflamme. Stream water could be partitioned into four distinct waters based upon event and flow path; however, similar division for lake water was not possible due to inconsistencies between tracer contents in the lake water. In terms of the major source of acidity, snow meltwater, stream water had an average meltwater content of 70% while near-shore lake water ranged from greater than 70% at spring melt commencement to less than 45% at the end. These high amounts of meltwater represent a severe hazard for the potential occurrence of “acid shock” of nearshore spawning grounds.