Koi stream - Tokyo Tower Aquarium, February 2016

Photo taken on the 2nd February 2016.

That appears to be a very tiny stand-off barrier...or is the depth perception of the photo tricky? Also, is that a turtle exhibit at the far end?

You're right - the barrier for the koi pool is very low, and at the end is an enclosed area for red-eared sliders and New Guinea snapping turtle; even the path by the pool here is out-of-bounds.