I havent really had a chance to get a good look myself as it's dark when I get home. Didnt notice it until I dropped the pond level several feet. It appears to be on bottom of pond only. Havent noticed a root system.
Doesn't look like Chara. Without a single stalk of the plant spread out in a shallow tray of water with a contrasting background and a good clear picture it will be hard to I.D.
9"x13" Pyrex dish, white paper underneath, 1/2"-1" water in the dish and a single stalk spread out so it's easy to see how the leaves/branches are growing off of the main stalk. Take a clear picture and I'm pretty sure we can ID it.