It's like a type of floating bog island that grows from piled up downed trees and other biomass and then breaks off from the main land.

Happens on lakes in Wisconsin. See [0] for a very interesting example of what happens when one gets real big and floats away.

[0] https://www.youtube.com/watch?v=X2AG6LAOBYo

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lifestyleguru 9 hours ago | parent [-]

How this biomass expands?! I don't think this happens anywhere else on earth. Usually tress downed into the water simply become bare trunks in the water.

	▲	chocrates 4 hours ago \| parent [-]
		The article states that it grows on driftwood so it is buoyant and mentions it is not that rare (not explicitly but it talks about it happening before)