Several turtle species make suitable pets for backyard ponds, including various sliders, painted turtles and map turtles. To be successful, you must select a species who will thrive in your local climate, and you must provide a pond large enough for your pets. In most cases, it is wise to select species native to your area.
Slider turtles (Trachemys ssp.) are among the best-suited species for backyard ponds. In the wild, some species live as far north as Illinois and Indiana, so they should thrive in similarly northern locations. Several different species and subspecies of slider turtle are suitable for pond life, including red-eared (Trachemys scripta elegans), yellow-bellied (Trachemys scripta scripta) and Mesoamerican sliders (Trachemys venusta). Red-eared sliders have become invasive in many parts of the world. Be sure to prevent your turtles from escaping into the surrounding habitat and check to make sure they are legal to keep in your area before acquiring one.
Painted turtles (Chrysemys picta) are attractive additions for most ponds, and are reasonably tolerant of cool temperatures. In fact, western painted turtles (Chrysemys picta bellii) live as far north as Canada. If your pond is not very large, opt for eastern (Chrysemys picta picta) or southern painted turtles (Chrysemys picta dorsalis), as they remain slightly smaller than the western and midland (Chrysemys picta marginata) subspecies.
Map turtles (Graptemys spp.) often adapt well to ponds, and make interesting captives. However, some female map turtles reach rather large sizes, so they demand large ponds with at least a few hundred gallons of water. Fortunately, male map turtles remain much smaller than females do, so those with small ponds can keep map turtles. Map turtles are not as likely to consume your pond plants as sliders or painted turtles are. They relish aquatic snails and other mollusks, which may help to rid your pond of the troubling invertebrates.
A few other species will live comfortably in a small backyard pond, but they have drawbacks that must be addressed. For example, stinkpot turtles (Sternotherus odoratus) are hardy reptiles, but they are not very visible to observers, as they will spend most of their time crawling around the bottom of the pond. Additionally, because they are not skillful swimmers, they need access to shallow water.
Softshell (Apalone spp.) and common snapping turtles (Chelydra serpentina) may thrive in large ponds, but they often have unpleasant dispositions, which can make caring for them difficult and dangerous. Additionally, these highly predaceous turtles are likely to consume virtually any other creatures in their pond, including small turtles and fish.