Carl Zimmer in his excellent blog, The Loom, which has just moved to National Geographic:
About 1800 years ago, a volcano in northern Nicaragua exploded. The crater formed by the eruption slowly filled like a rain barrel. Eventually the water rose high enough to warrant the title of lake. Today it is called Lake Apoyeque. Although Lake Apoyeque is over 300 feet deep, the rains have a long way to before they reach its brim. Lake Apoyeque remains ringed by volcanic cliffs towering as high as 1200 feet. And yet, despite its young age and its remote location, it is filled with fish.
For thirty years, Axel Meyer, an evolutionary biologist now at the University of Konstanz in Germany, has journeyed to Lake Apoyeque and other lakes of Nicaragua to study the evolution of their fish. He and his colleagues have caught cichlids and sequenced their DNA. By comparing their genes, the scientists can work out how the fish spread across the country. At Lake Apoyeque, for example, they found that the cichlids shared a number of mutations with the cichlids of Lake Managua nearby. The fish of Lake Apoyeque have accumulated relatively few mutations of their own. Meyer and his colleagues studied those mutations to estimate how long it took for their genetic diversity to evolve. They concluded that the cichlids came from Lake Managua to Lake Apoyeque only about a century ago.
There are forests and cliffs dividing Lake Managua and Lake Apoyeque, and no one can say exactly how the fish leaped over them around 1900. One likely route is a water spout. Water spouts are known to pass over Nicaragua, and it’s possible that every few thousand years one of them happens to suck up fish from one lake along the way and drops them in another.