Well I rescued a couple turtles that I thought would be a great addition to my beautiful pond. Like you I had frogs, snails dragonflies plants and koi with long flowing tails.... well those turtles tore up and ate all the plants, snails, frogs and scared the koi and damaged many of their tails. I would suggest against the turtles unless you have a very very large pond.

I've had eastern painted turtles in my pond for years. They never bothered my goldfish or frogs. They will take a bite out of a lily once in a while, but they certainly don't destroy my pond plants. I've seen koi do much more damage. Koi require a special pond while painted turtles can exist in a water garden.

Turtles like to travel and will leave your pond if you don't secure them. I use plastic fencing supported by rocks. They need basking areas, so you should have some rocks or land for them. If you feed them turtle pellets, they won't feed off of plants as much. My turtles also love watermelon.

Painted turtles are native to my area, but they would not survive a cold winter in my pond. They dig into the mud at the bottom of natural lakes and ponds in November and hibernate until April. They can't do that in a pond with a rubber liner. I keep two turtles in a large indoor aquarium during the winter. If you can't do the same, I would forget about turtles.

I have a red eared slider in the pond that came with our home. He has been doing well for years. He does bite off the leaves of any water lilly I try to put in as soon as it sprouts, so I have had to give up on them. He hibernates in the winter and has never bothered the fish.(koi and goldfish) He is the first one to the edge to get the food when i feed the fish. If you can live without the lilies go for it.

Turtles will wander. A friend in LA has had his neighbors return his. They can dig and climb more than you'd think too.

They do require excellent filtration as they produce manure that in quantity smells really bad. It depends on how big your pond is and what kind of filter you have to clean if this is going to be a problem. Pond muck/filters always smell but one with turtle poop reeks to high heaven.

They do have specialized requirements for hibernation and basking as well.

There are many turtle rescues around with animals for adoption because many buy them and give them up. Or worse, release them. Red ear sliders are an invasive species in the Western US where they are causing extinction of native turtles. This is one reason besides salmonella that you cannot buy little turtles anymore like you could in the 60's and 70's.

Thank you to all for your postings! I've decided against the turtles for all the reasons you stated. I've noticed my pond has been losing water and traced it to my waterfall weir that the water is seeping out of!!
That should occupy some of my available 'pond time' fixing it.
Thanks again to all and happy ponding!