Here is the first
of three photos Kim Webb took of a zebra-mussel-infested boat that came
into California last spring. From this angle the boat looks clean.
The boat bottom
was clean, but zebra mussels were thick under the trim tabs. You can see
the trim tabs in the photo above of the rear of the vessel. They are sagging
slightly.
This close-up photo is what you could see if you
peered under the trim tab. Zebra mussels can be seen attached to the bottom
of the boat between the trim tabs and the hull.