That's what algae looks like when it's dead. Much
better than you or I would, I'm sure. It'll settle
to the bottom into silt, and stink up the place like
a couple of bean-eatin' guys at Joe's on Friday night.
If this is settling in your main pond, that's especially
bad since it'll be hard to get out (bottom drain would
take care of it easy). If you have a well-(or luckily-)
designed filter, this accumulates only in the filter
(or upper/veggie pond) and is easily dealt with.

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'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`'`''`'`'`'`'`'`'`' `'`'`''`'`'`'`'`'`'`'
SLOTHEAD