jeff, water oak is just one of the many types of oak tree that we have growing round here. I used it due to the fact that it was convenient, ie.. the tree fell over in a storm and I didnt want to burn all of it and I felt that a "currently living" limb from a tree would last lots longer under the water of my pond than an old half rotten one. If there is something toxic about them please speak up so I can get them out of the pond asap. as far as the type of algie bloom? I dont have a clue. All I can say is it seemed greasy looking with lots of small bubbles in clumps on the surface of the water.

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