Birch Bark to seal ponds?

I was wondering if anyone has used birch bark to seal a pond?

I would think it would decompose.

    ¿Isn't the gley that seals ponds formed with anerobically underwater or under pond liner plastic or whatever decompsing vegetable matter?

    ¿Did not native americans use birch bark to boil water in?
    I have put in Spanish question marks because it can amuse people from other countries, they put in question and exclamation marks before and after sentences. agri rose macaskie.

I wonder whether the OP was referring to birch bark tar ? Sounds interesting.

Birch bark will last for centuries in the right conditions (and permanently waterlogged, in the dark, may be close to ideal). However, making a waterproof layer seems difficult. Even from large, straight, knot free threes, the bark sheets won't be very big, and the seams between the sheets will leak. Birch bark was used under turf roofs here in Norway, this works because on a roof you can overlap the sheets so that water runs off. I've seen birch bark apparently used as a moisture barrier under sill beams and possibly under floors in remains of medieval houses in Oslo, I assume the bark would act more as a capillary break in these situations - it may prevent the sill beams or clay floors from actually sucking moisture from the ground below. These anecdotes are not directly relevant to the original question, but they do show that birch bark will last a long time in certain conditions.

Birch bark tar seems unrealistic. I've never heard of it made in large quantities the way pine tar was. I've no idea how much you'd need to waterproof a certain area of pond side/bottom, or if it would work at all, but I have read that birch bark yields at most 10% tar pr weight - collecting and processing enough bark to make even a bucket of tar seems prohibitive. It is only the flaky outer layer of bark that is used, in other words a layer of at most a few mm.

Yes, and also if you did seal a pond with any kind of tar, I imagine you'd get a bunch of hydrocarbons and other interesting chemistry leaching from it and polluting the water. I know the smell of birch bark tar, and can't imagine it's altogether healthy...

A thought about using sheets of birch bark, though: the seams between the sheets will leak, yes, but if the bark sits on a layer of compacted soil, and again has a bunch of soil (and water) on top of it, pressing the seams shut, maybe it'd make for a better seal than compacted soil on its own? The cross section of the downward path available to the water would be smaller, after all. Still don't think it's very practical, but I imagine it might just be possible...