Hi Rockey2. I commend you for being so responsible - most people would not give such things a second thought and it's refreshing to hear that you do. Yes, releasing them by the lake would be fine. I've seen American Green Treefrogs (Hyla cinerea) even breed in large water bodies so the lake side should not be an alien experience to them. I would suggest letting them go in the evening around dusk - not as hot and not as many predators around (birds are a big one for froglets).
Best of luck.
-John