http://www.amnh.org/about-the-museum/press-center/fish-evolution-shaped-by-intense-rapids
Cichlids of the Telegramma genus are evolving rapidly in waters of the Congo river due to the intense hydraulics of the river's rapids and deep canyons. The study, led by scientists from the City University of New York, Fordham University and the American Museum of Natural History have found that populations reside in "neighbourhoods" separated from one another by turbulent flowing water. Fishes living in relatively close proximity, less than a mile away from their relatives, are exchanging few genes, resulting in speciation. Please see the above link for more information and the associated Molecular Ecology paper.
Alter, S. E., Munshi-South, J. and Stiassny, M. L. J. (2017), Genomewide SNP data reveal cryptic phylogeographic structure and microallopatric divergence in a rapids-adapted clade of cichlids from the Congo River. Mol Ecol. doi:10.1111/mec.13973
