The Ankhora Water Vessel is the thirty-second treasure that can be found in Uncharted 2: Among Thieves.
The Ankhora Water Vessel is found in Chapter 7 - They're Coming With Us . If you thought that there must be a treasure around the area where the team needs to cross the river, then you thought correctly. It's a well-hidden one, though—it's located at the top of a pile of rubble against the far river walk. Climb down the stairs on the near side of the screen, and instead of using the cars you nudged free to cross the other side of the river, go leftward and jump onto a pile of rubble. From here, you can cross over to the front of the rubble pile in the middle of the river (though the current won't let you actually climb atop it), and you can continue to cross to another pile of rocks and rubble in the far corner. En route, you'll see the glimmer of what you're looking for, as there is a treasure sitting atop the last-mentioned pile of rubble. Grab it, and then backtrack across the river towards the cars to proceed.