This was an interesting find on the outskirts of Dallas,TX. A part of a small natural peserve setup by the cities in the area. This pool isn't poluted by humans nor does it have a alge bloom the water is just this color. Why? The small note about it at the trail head says tha the most likely cause is the abundance of a mineral in the area, and the springs in which feed the pool must run through or along a vain of the mineral.(I say mineral, because I don't remeber what it was, but I do recal that it creates a very soft crystal which can be found throughout the natural area if someone is willing to dig a little.