How are you turning a 20 acre lake into a 40/50 acre lake? I bet it's a huge undertaking!
Where I live most lakes of this size are fed with a small creek. The watershed that feeds the creek usually has multiple farm ponds in the acreage. I'd suspect that high water events let's fish to be stocked from those ponds. Unless your lake is somewhat public then someone could have bucketstocked it.
19 acre watershed pond
LMB, BC/WC, Bluegill, Crawfish, GShiners
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