WOW I can't imagine 400 feet! I assume only trout have been caught in that lake. I would find out what the forage base is for a start. Then try to improve the lake for the forage fish and the rest will return assuming there are still native trout in the lake. It's going to be a whole new ball game for sure. I would try micro fishing and see if you can catch any bait fish to learn whats in the lake.

I would pass on the idea of draining it down and starting over LOL!