Some of the biggest and worse seas I have ever been in were in Lake Erie -- large and very shallow lake (average depth is only 30 feet) where the waves are extremely steep.

Worst one was in Laser in the 70s at I-LYA Bay Week. We were sailing along going to the weather mark when a cloud that reached all the way to the water came at us. From out of the cloud came the first of the waves and it was higher than my mast. Pretty much knocked the hell out of the fleet. Although, with a Laser is was just as easy to just stay on its side.., safer.
Rick