Agree with JL on both issues:

Provided the pond basin isn't allowed to remain dry for an extended period of time during dry Summer heat, you shouldn't have any concerns with liner cracks and subsequent leaks.

Cool water species fishery can be achieved in your region [I work with several clients in the NE/KS/IA/MO region with cool water species fisheries] but you'll need to drain, nuke, and begin fresh.

Many men go fishing all of their lives without knowing that it is not fish they are after. ~ Henry David Thoreau

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