This looks like a pool but it’s actually a river flowing through the Phong Nha national park in Vietnam. If you look closely you can see the bridge we walked across as we explored the area.
I’ve mentioned before that when we visited Ha Long Bay we actually stayed on Cat Ba island and explored the surrounding area by kayak. There was all sorts of activity on the water from small fishing boats to floating villages.
I think I actually took this photo from the tour boat that transported us to the island, but I’m not sure.