First, get more detailed information about this lake from the responsible authority. Does it have a natural inflow and outflow? What were the highest water levels in recent decades? I would try to find out whether the lake is geologically capable of swelling that much. If it lies in a basin and has a natural overflow with essentially unlimited drainage capacity, you do not have to consider this risk as a central starting point for planning. Our city has published an online map that marks and shows flood hazard areas by color. This way, you can immediately see which areas could be flooded by the river that runs through here. We ourselves are 50m away from such an area, so we must practically always expect that this could happen one day. Although not like in the Ahr valley, in 1999 everything was flooded just 20m from our doorstep here as well. You can really only answer this question yourself if, as said, you have closely examined the conditions and then talked about it with an expert.