A Masonry Dam is build out of individual stones or bricks. The Wikipedia link says that it is "sometimes" joined with mortar, and has a cite for it but the link is 404 dead.
Is that really true? How could a masonry dam not require mortar? The dam needs to be water-tight against a wall of water, which has larger pressures at the bottom. I don't see how the individual blocks could be so tight and perfectly-fitting to stop water at high pressures.
I was unable to find a single example of a masonry dam that explicitly does not use mortar. I guess I'm missing something. Is there some other common seal mechanism besides mortar?