There are many turtles that call the pond their home, but none will spend their time in the deep water of a pond. If you plan on keeping turtles then give them a shallow area (1-2 inches deep) where they can sun themselves and rest. Keep in mind turtles, like frogs, are predators and will eat your smaller fish. Turtles have also been known to take bites out of tail fins and anything else they can get their mouths on including the body of a big fish, so if you see a chunk missing from your fish blame your turtle first. The most common turtles are known as Red Sliders and grow to about 10" at maturity. You must also change the water frequently as turtle feces contain bacteria know as salmonella which can make you quite ill. As turtles grow their appetites turn towards your plants so keep them fed or they will eat their home.