If everyone had their choice would you use treated or cedar.
I would use pressure treated posts rated for ground contact before I used cedar. Perhaps even rated for "ground contact critical use" The newer AC2 preservative treatment which replaced CCA is much less risky to health. But if you don't want it in your pond I understand.
Osage Orange/hedge would out last us all but would be more difficult to find enough somewhat straight ones. For my dock I used big utility poles, but was able to install them prior to the lake being filled.
