Since the New Synthesis, most migration-selection balance theory predicted that there should be negligible differentiation over small spatial scales (relative to dispersal), because gene flow should erode any effect of divergent selection. Nevertheless, there are classic examples of microgeographic divergence, which theory suggests can arise under specific conditions: exceptionally strong selection, phenotypic plasticity in philopatric individuals, or non-random dispersal. Here, we present evidence of microgeographic morphological variation within lake and stream populations of threespine stickleback...