Assuming that you live within the natural range of the turtle species you keep -- or an area with comparable climate -- outdoor turtle ponds are an excellent way to house your pets. You must be sure that the pond is large enough to allow your turtle to engage in natural behaviors and that it provides ample basking opportunities. A quality filtration unit will keep the water clean, and a sturdy fence surrounding the area will help keep predators away from your pets.
You can build backyard ponds in several ways, and most methods will work fine for turtles. After excavating the depression, you will need to use either a prefabricated pond liner, and flexible pond liner or poured cement to make the hole hold water. Concrete provides the most durable surface. Flexible pond liners are not as durable, but they are easier to install. Prefabricated liners are simple to install, but you cannot alter their shape.
Size and Shape
Although large species, such as snapping turtles (Chelydra serpentina) or softshell turtles (Apalone spp.) may require more space than this, most common pond turtles require about 50 to 100 gallons of space for each turtle, depending on the species. It is always better to provide more space than necessary to avoid overcrowding your pets.
Most turtles will adapt to ponds of virtually any shape, but some shapes offer advantages over others. For example, you could use a relatively long and narrow pond to take advantage of shaded and sunny areas, thereby giving your turtles access to a wide variety of temperatures. Additionally, by keeping one dimension -- in this case, width -- relatively short, it is unlikely that your turtles can swim farther away than you can reach at any given time. However, this also means that should predators access the pond, your turtles will have a harder time evading them.
If you intend to leave your turtles outdoors year round, the pond must be several inches deeper than the local frost line, so your turtles can survive under the ice. The pond need not be very deep if it will never freeze, or if you plan to bring your turtles inside during the winter. At least 12 inches of depth are necessary to prevent your turtles from slamming into the bottom of the pond, should they dive in suddenly. If you keep turtles that are not strong swimmers -- such as musk turtles (Sternotherus odoratus) -- include a large shallow section to ensure your pet can reach the surface for air.
Situate your turtle pond in an area that offers both sunlight and shade, if possible. If you do not have such an area, place the pond in direct sunlight, but place plants, trees, rocks or other objects in such a way that they shade a portion of the pond. If you live in an area prone to heavy rains and flooding, it is wise to avoid placing the pond in low spots of your property, as it may cause the pond to overflow.
Whenever possible, try to place the pond in close proximity to your home to discourage predators and unauthorized people from hanging around the pond.
Basking and Digging Opportunities
You need to provide your turtles with places in which they can crawl out of the water and bask in the sunshine. Semi-submerged logs and branches work well in this capacity, as do stacked rocks. You also can make sloping "beach" areas, along the shore, which your turtles can use to exit the water and soak up the sun.
Provide your turtles with an area near the pond that features a substrate suitable for digging, such as topsoil. Some turtles may forage in the substrate, while others may prefer to bury themselves on land during the winter, rather than hanging out at the bottom of the pond. It is imperative to provide all female turtles -- even those housed without males -- with such an area, as they will use this area to deposit their eggs. Without access to such a space, the turtles may become egg bound.
While some keepers elect to skip the use of a filter, others rely on filters to help keep the water clean. However, if properly established, the pond's natural cycle may keep it sufficiently clean. If you elect to use a filter, opt for one rated for a pond twice as large as yours. You will need to perform maintenance on the filter from time to time, so put it in a place you can access it easily.
Despite their strong shells, turtles often end up looking down the business end of many common predators, such as raccoons, coyotes and domestic dogs. The best way to protect your pets is by erecting a fence that completely encircles the pond and surrounding land area. The fence should penetrate the ground to a depth of at least 12 inches to keep critters from tunneling underneath, and it should feature some sort of protective top as well, as many predators are skilled climbers.