Abstract: Seasonal succession of phytoplankton distribution and community composition are well-established in aquatic ecology. However, localized peaks in phytoplankton abundance—patchiness—can deviate from expected trends. To better understand this variability, I analyzed vertical profiles of phytoplankton distribution across fifteen lakes in southeast Michigan over three field seasons (2021-2023). I focused on four major phytoplankton groups—green algae, cyanobacteria, diatoms, and cryptophytes—and examined how their abundance varied with depth, temperature, and season. Detailed case studies from six representative lakes highlight how basin morphometry influences thermal stratification, shaping phytoplankton patchiness and concentration over time. Green algae were typically most abundant at the surface during summer months, though several lakes exhibited benthic green algal peaks. Cyanobacteria, diatoms, and cryptophytes showed greater variability across depth and lakes, with cryptophytes often displaying more consistent abundance throughout the water column. Temperature profiles followed expected seasonal trends, with strong stratification in summer and mixing in the fall. These results emphasize the importance of considering lake-specific conditions in driving vertical phytoplankton patchiness.