Great question. Overall, Mercer Island (and Lake Washington) homes have minimal risk of flooding. That being said each property is unique and you want to be confident that any home you purchase is not at high risk for flooding. Not just the lake flooding, but also surface water runoff due to heavy rains and the gradiant of the land.
Mercer Island is a "glacial hillock", so terrain rises steeply from the lake, so non-lakeside properties are located 10s-100s of feet above the lake level, so no flooding concerns.
