The Louisiana red swamp crayfish (Procambarus clarkii), is quite popular in the southern states, but with predators such as fish, amphibians and small mammals the numbers are maintained; however, there is a different story for many African nations.
This gloriously colored animal was brought into Africa in the 1970's where they were used to increase available food for natives and Scandinavians. Eventually, after the market for the crayfish went down, use for this crustacean was found in ridding dams of disease ridden snails.
Many countries in Africa are currently experiencing the overpopulation of the red swamp crayfish and it isn't just the numbers that are scaring locals. These crayfish are taking over! (Sounds like a line from a 1950's horror film). They have been documented in lakes and rivers in Uganda, Kenya, Rwanda, Egypt, Zambia, the Seychelles and South Africa consuming small fish, eggs, mollusks and even other crustaceans. Researchers are concerned that these crayfish will widen their range and begin to take over lakes and rivers containing species found nowhere else in the world.
Unfortunately, there is no easy fix to this problem. These African countries do not have the funds or equipment to track the spread of the crayfish. Erecting barriers to prevent the movement of the crayfish (just as is being used for the invasion of Asian carp in the United States) would help immensely; however, the precise location of these critters would have to be known. It has also been suggested that trapping and poisoning the animals would also help. I find that this would have to be done very carefully as to not pollute any of the water and cause bigger issues than getting rid of a pesky crayfish.
Alas, until there is an efficient way of discovering how to maintain the population of Procambarus clarkii in Africa, the only thing to be done is keep hunting the hunter.