I'd go deeper than 20 feet -- that shallow, and you could see vast stretches of the thing completely dry in a bad drought year.


The effects of your inland sea will depend on surrounding geography and climate. I'd actually suggest looking at the effects of the Great Lakes of North America on the surrounding climate, growing regions, etc, if you're going to have a temperate land around this island sea. Lake effect snow is something many people haven't heard of, for example.

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