Estimates of the numbers of young-of-the-year and mature (age-groups I and older for the brook trout, and 9 inches and longer for the brown trout) brook and brown trout present in Sections B, C, and D of the Pigeon River were made each September 1949-60. Correlation coefficients (r) were calculated for the numbers of young-of-the-year trout and groundwater levels in October as measured in feet below land-surface datum at an observation well within the Pigeon River drainage. Calculation of the difference between the average minimum discharge (in cubic feet per second) at two streamflow gaging stations on the Pigeon River indicated the well measurements were reflected in the flow data. For the 9 years of available data, 1949-57, there was a highly significant linear correlation between numbers of young-of-the-year brook trout and groundwater levels; for the brown trout no correlation was evident. During years of high groundwater level, large numbers of young-of-the-year brook trout were present. Correlation coefficients calculated for the number of mature trout estimated to be present each September and the number of young-of-the-year trout present the following September, for 11 years of data, 1949-60, were nonsignificant for both brook trout and the brown trout. Analyses of variance of regressions of young-of-the-year trout on groundwater levels and mature trout for the years 1949-57 agreed essentially with the correlation coefficients.