Seems like the problem is poor water flow in and out of the pool. The property I grew up on had an artificial pond that was put in by the previous owner of the land. There was a functional inlet/outlet that kept fresh water flowing in and out from the natural creek next to it.
However one year a small part of the creek got blocked of which was where water flowed in for the inlet. Unfortunately that part of the creek was not on our property. My parents asked the neighbors if we could remove and clean up blockage. They said no. Over the years the pond gradually dried up and now there's nothing left. The best feature of the pond was a tiny, and I mean really tiny, island that large birds like Canadian geese and even the occasional stork used a stopover during migration. However because of the blockage the water starting go bad then drying up, the birds stopped appearing.
Anyway the situation with the Reflecting Pool may be a lack of inlets and/or outlets or that the plumbing for both are too small to handle the amount of water that flows in and out of the pool.
