IIRC the theory is grass provides a substrate for aquatic plants and invertebrates to live on.

We just planted down about 2' below the eventual waterline, for erosion control before the pond filled. I suppose that's deep enough in most ponds to cover the light-penetrating zone in case there's anything to the above theory.


"Live like you'll die tomorrow, but manage your grass like you'll live forever."
-S. M. Stirling
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