Larvae of the bloater, a coregonid fish, were sampled systematically in southeastern Lake Michigan from April 9 to Aug. 22; additional sampling was done on Oct. 15. Collections were made with a 1-m plankton net of 0.66 mm mesh, towed obliquely through various strata over bottom depths from 5 to 88 fathoms. Bloater larvae were scarce in early April, increased to maximum numbers in late June and early July, were scarce again by late Aug., and absent in mid-Oct. Hatching appeared to be at its peak about mid-June. The larvae were present in all areas where the lake was 10 fathoms deep and greater, but the majority (83%) were caught between 40 and 60 fathoms. Most were found near bottom, except during the April and early May collections. About 96% were taken from strata in which the maximum temperature was not more than 4.7 C. There was evidence that weak swimming ability of the larvae as well as water temperature influenced vertical depth distribution. A limited but definite upward vertical migration occurred at night.