Shell length-frequency distributions of generation cohorts of zebra mussels sampled from settlement plates at (A) Belton and (B) Stillhouse Hollow Lakes. The horizontal axis is sampling date and the vertical axis is shell length in millimeters. Horizontal bars indicate percent of the total sample at each 0.1 mm in shell length. White lines connect mean sample shell lengths for different mussel settlement cohorts, i.e., 2019 fall cohort (upper line) and 2020 spring cohort (lower line). Vertical white bars about mean cohort shell length points are standard deviations.