This is übercool. Researchers from American Museum of Natural History first profile the hydrological features of the Lower Congo River. They find out that there are canyons which are hundreds of meters deep. These canyons are separated from each other via strong currents. So for a fish getting in one of them there is almost no way out.
They then collect fish of the same species - where species is defined from the way they look - from different canyons. They analyze their DNA, and they see that evolution is in action, and the difference in their genome sequences correlate with their geographical location. Speciation has not started, but it is on the brink of starting.
This is my friends, Evolution in action.