I'm pretty sure that's one of the Asian Brown Tortoise, I've noticed on recent visits that they are spending more time in the water. On recent visits, I've only seen the Giant Asian Pond Turtle on the land area rather than in the water with the Batagur and fish.
This appeared to have a much smoother, less-domed shell than the other tortoises in the exhibit, but that could be caused by being underwater.
Edit: Having compared images on google, based off the head shape, shape of the scutes, and the colour of the plastron, I'm still more inclined to consider this Heosemys grandis.
