Depending where you live, putting an aquatic turtle outdoors might be something you can only do for a few months in summer. You need to consider the natural range of the species you have. For example, red eared sliders are quite hardy and adaptable. Some other species need warmer temperatures, so you must keep the natural habits of your turtle in mind when deciding to house them outdoors. In warmer climates aquatic turtles may be able to live outdoors year round. It is also possible to hibernate some species in an outdoor pond, although this is not without risk (see next page).
Safety and Security
Aquatic turtles kept in outdoor ponds do need to have secure fencing. There should be a fence around the pond (at least 2-3 times higher than the carapace length of your turtle, and sunk into the ground 6-10 inches to make sure there is no chance of escape). The fence should have a solid base so turtles don't get caught up in wire. This fence is meant to keep turtles in, since they will wander in search of a mate. It also helps keep predators out. You may also want to consider a cover (e.g. chicken wire) over the pond area to protect your turtles, especially if predators like raccoons come into your yard. Hatchlings and small turtles are extremely vulnerable to predators so are best kept indoors until they are a good size.
What Does a Turtle Pond Need?
The depth of a turtle pond will vary a bit depending on the species, but should have a relatively large surface area (provides better oxygen levels in the water). Red eared sliders and some other turtles can handle a deeper pond, while some turtles prefer to be in shallower water, so again consider the natural habits of the turtle species when planning your pond. Try to have varied levels of water with slopes between them. A shallow area where the turtle can sit in the water with its head out of the water is desirable as well. You can used a preformed pond liner, a flexible pond liner (get the heaviest one, as turtles have fairly sharp claws), or any large water vessel such as a plastic kids pool sunk into the ground.
Basking area: this is very important. You must provide a log, plank, bricks or rock for the turtle to get out of the water and bask in the sun. Arrange your basking area so it is partially submerged so your turtle can easily get out of the water onto the basking area. The basking area should get sunlight for a good portion of the afternoon.
Turtles do like to get out for a stroll, so it is good to include some land around the pond in your fenced area.
Hiding areas: provide hiding spots and shaded areas both in the water and out of the water. Large leafed plants (aquatic or on land) work well, as do clay plant pots placed on their sides.
Plants: keep in mind turtles can do a lot of damage to aquatic plants (both by eating them and swimming around them) so if your pond plants are a source of pride adding a turtle to your pond might not be the best idea. However, water plants provide shade and shelter as well as extra food so are a great addition to turtle ponds. Water lettuce, water hyacinth, fairy moss, anarchis or fishweed (sometimes called Elodea), Cabomba, and tape grass are recommended. Marginal plants like dwarf cattails, dwarf rushes and dwarf papyrus also help naturalize the pond edge.
The levels of oxygen in the water can be improved by the addition of waterfalls, fountains, external filters and airstones. This is especially important in cold weather.
What About Fish?
One great advantage to larger ponds is that you can add feeder guppies and goldfish and your turtle can be kept busy hunting. However, if you prefer ornamental fish like koi, caution is warranted. Some turtles are quite avid hunters and may even try to nibble on larger fish, which can cause injuries to your fish (especially fins and tails). It is somewhat individual, as some well-fed turtles won't bother chasing fish, while others have a stronger hunting instinct. Also, water quality can be harder to control with turtles in the pond, which can affect the fish.