You can see the effect of humans at Lake Victoria too. Lake Victoria is between Kenya, Tanzania and Uganda in East Africa, and it is one of the biggest lakes in the world. The lake was home to about three hundred species of little cichlid fish and sometimes new species of cichlid appeared. But in the 1950s, the countries near the lake needed more food. From the River Nile in Egypt they took two of bigger fish - Nile perch and Nile tilapia - and put them into the lake. The perch are the little cichlids and soon many species were extinct. Tilapia do not eat other fish, but they ate the food of some cichlid species. That also helped to kill the cichlids.