If wild pond turtles have homesteaded your pond, it's because they've found it to be an ideal environment with adequate shelter, hiding places and a good climate. If your pond is clean and healthy, abounding in natural food items, the turtles probably don't need food from you. If you feel the need to feed them, however, keep their specific needs in mind. Wild pond turtles are omnivorous and opportunistic feeders. They aren't terribly picky and will eat naturally occurring bugs, small fish, pond weeds, algae, water lilies, frogs, frog eggs, even carrion.
Feed wild pond turtles no more than once daily and at approximately the same time each day. Toss the offering into the water because most aquatic turtles must consume food while it's at least partially submerged in order to swallow it. Don't just leave stuff on the bank, where it may be overlooked or ignored and could attract rats and raccoons.
Toss a couple of commercial turtle or koi pellets into the water near the wild pond turtles. Don't be surprised if they quickly duck under the surface to hide. They've probably never seen people before and will think you're a huge predator. Step back a few paces from the water's edge, squat down and be quiet and still. Within a few moments they'll test the offering. When they find the pellets to their liking and completely consume them, give them a couple more. Within a few days the turtles will get the idea that your presence means food and you're not a threat.
Use a small-mesh dip net to remove uneaten food after five or 10 minutes, even if the pond turtles may still seem to be hungry. Don't try to feed these wild animals a complete diet. That's not your job, nor is it good for them. Your pond is self-sustaining and has everything the turtles need, or they wouldn't be there. The idea is to give them treats so they will welcome you and be happy to see you--not to make them totally dependent upon you for their livelihood.
Choose healthy food treats appropriate for wild pond turtles. They like insects, but don't kill houseflies for them. Flies not only carry diseases, but eggs that will hatch into parasitic organisms in the gut of any animal that consumes them. Offer instead highly nutritious commercial turtle or koi pellets as your first choice. They'll also take fresh vegetables and dark, leafy greens. Don't give them iceberg lettuce, which have almost no nutritional value. Turtles also enjoy fruit. Never give them meats, fish, poultry, cheeses, eggs or other animal products.
Cut or chop foods into bite-sized pieces for wild pond turtles, particularly those under 4 inches long. Youngsters prefer these smaller portions because they're much easier to eat.
Purchase live foods such as mealworms, earthworms, crickets, minnows or feeder goldfish and guppies if you wish. Many live foods can carry parasites and infectious diseases and bacteria, so do business only with reputable retailers. Rinse all worms with cool, running water before offering them to your pond residents.
Float plastic bags containing small fish in the pond water for about 15 minutes before releasing them. This will give them time to adjust to the temperature of the water, which is likely to vary greatly from that of the water in the bag. The immediate shock of an extreme temperature change will kill fish within minutes. Besides, it's good for the turtle to have to chase its living dinner around a little. Don't worry if the live fish aren't consumed immediately. Even if they do die, the turtles will find and relish them.
Feed wild pond turtles only throughout the warm months. Stop offering food when the weather cools and the turtles show little, if any, interest in eating. They'll typically fast throughout the winter and resume normal eating habits as temperatures warm in spring.