Bug:
Kelp growing into flowing water creating source blocks.
Outcome:
Kelp growing into running water blocks creating new source blocks above a lake.
Lots of kelp was added as decoration and many of them created source blocks above the lake. These source blocks merged causing much of the lake's water level to become a block higher.
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Yes, we believe this is exactly the issue.
Is this the intended effect of kelp?

nice farm
Does MC-133354 describe your issue?