These data, collected during 1942-1944 by Dr. David C. Chandler, describe the density, biomass, and growth of a now extinct population of burrowing mayfly nymphs (primarily Hexagenia limbata) that lived in the sediments of western Lake Erie near South Bass Island. The growth dynamics of this population have not previously been documented. Female nymphs grew faster than males and were about 4 mm longer than males at emergence each year. Significantly fewer nymphs were collected in 1943 than in 1942 or 1944. Before they were extinguished by low dissolved oxygen in 1953, mayfly nymphs were abundant (about 350 weighing 10 wet g m-2) near this island and throughout most of western Lake Erie. The western basin once supported a biomass of 9.6 t · km-2 or at least 17,600 metric tonnes of mayfly nymphs. If burrowing mayflies recolonize the sediments of western Lake Erie, these data could be used to assess the extent of their recovery.