Hi, I am currently building a natural swimming pool following the methods of David Pagen Butler, if people are familiar with him. We are planning to put untreated oak beams on the top of the retaining wall, submerged fully in the water. We are a little worried about the tannins in the oak as we think they may make the water really brown and not look nice at all. Has anyone any experience of doing this, please? Many thanks for any advice.