Sympatric speciation in a glacial lake may actually be due to micro-allopatric or micro-parapatric speciation. By studying genomic islands of divergence, researchers found that the divergence between two fish species in Lake Sunmcuo happened 20-60 thousand years ago. They identified 54 large genomic islands related to olfactory receptors, suggesting speciation with gene flow. These findings support the idea of parapatric speciation, where adjacent habitats allow for both divergent selection and gene flow during speciation.