esshup's link to "natural swimming ponds" is a very good idea in many circumstances.
You do not need to build a 30' tall dividing wall. You could use an excavator to create some long, narrow trenches outside of your current pond boundaries for your plant filter system. I think the longer the flow path of your recirculated water, the better the filtering efficiency. However, a 100'x125' swimming pond is a lot of surface area to filter. That would require a lot of surface area for your adjacent "filter system". Don't know if your property has the room for that, or if your family would like that visual frame.
However, if you have a larger budget, you could build your plant filter system as a series of terraces with cascading water falls if you have a hillside near the pond. That would give it a unique style to create your required large filtering system.
Good luck on your improvements to your new pond and property!
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