problem figuring out how to "lower" a fall from upper to lower pond

[Mmathis]

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[mgmine]

Would it be easier to raise the upper pond a few inches? Even though the stones are mortared it seems easier than trying to lower weir area. Simply adding stones to the bottom of the upper pond would raise the water level then if needed add additional liner on the sides and maybe another level of stone at the top.

 

[lachancesare]

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View attachment 99429

Yes. Absolutely!
And here is a sample of my progress addressing it.
There were not 3 layers of liner but 4!!!!
But I'm (hopefully) getting to those cinder blocks!