Update: See this article in the Seattle Times
KOIN News 6
RIDGEFIELD, Wash. - A trailered houseboat was decontaminated after shells from a highly invasive mussel were found on the stern.
The 75-foot-long houseboat was on its way from Missouri when it stopped at the Washington State Patrol weigh station near Ridgefield. Officials discovered dried shells and held the vessel overnight.
Fish and wildlife agents call zebra mussels the biggest living danger to our ecology and economy.
Good catch! Kudos to the State Patrol for spotting the problem and to KOIN for reporting it.