The stratigraphic record of 137Cs activity levels found in Pitt Lake, British Columbia, mimics the radioactive fallout values for 137Cs and 90Sr recorded in milk from the adjacent Fraser Valley. The Pitt Lake record closely parallels the fallout values obtained in England, Alabama, and Lake Michigan. The presence of 137Cs in Pitt Lake sediments is unequivocable evidence for modern (since 1952) clastic deposition. Calculated sedimentation rates as great as 1.8 cm year−1 were made using the 137Cs technique. These values substantiate previous estimates based on varve thickness. The technique is shown to be a useful tool which can quickly and reliably determine modern lacustrine sedimentation rates.