Agree with oldjeep. We have them in most lakes in Indiana and I've never seen them on a ski boat or heard of them being a problem for the boat itself- more that they spread from lake to lake and become a pita on docks, structures, beaches, industrial water intakes and such. My current ski lake does not have them and we don't let boats that have been used on other lakes be launched at the ski lake. The things are razor sharp and my previous ski club had them- needed to use gloves for course maintenance or they would eat up your hands. Kids had to wear water shoes to avoid feet getting cut. I definitely wouldn't be scared to visit a lake that has them. One of the bigger reservoirs (Brookville) that I visit I really only see them if I'm fishing for walleye and hook a rock that's covered with them.