I already have those too. The chest I circled is north of the Lakebed Temple, but that's in a random spot in the lake and there's nothing underwater there. It also happens to be directly under the bridge, so it could be that it's actually above the bridge (on the north part) but I don't see...
The waterfall is on the far west of Lake Hylia, but the chest is directly north of Lakebed Temple according to the map, but there appears to be nothing there (neither under or above the water). I tried your waterfall idea anyway, but the Cuccoo minigame wasn't even close to reaching it (using...
I've always been pretty confident that I've gotten all the treasure chests in TP in my playthroughs of older versions, but this time I actually decided to check, and I found out I was missing one according to the above map (there's also a few grottoes in Eldin Field with chests that are not...