I haven't checked my local ramp this year, but I hope there are warning signs posted all around this lake. Zebras like warmer lakes, but there is another -- equally bad -- exotic mussel that likes waters down to 46°. Didn't one state (New York?) require ramp-boaters to spray their boats and trailers before launch?
The problem isn't so much that zebra mussels will attach themselves to any firm surface and will clog water intakes, they clog boat
engines.
This Michigan site suggests that boaters from infected lakes run their engines twice a week for 10 to 15 minutes at top speed!
http://www.miseagrant.umich.edu/pubs/on/msg-94-713.html
.