How did mussels sneak into California, despite decades of state shipping rules?

Earlier this week, in Napa County, the Bureau of Reclamation sent out a news release stating that Lake Berryessa had implemented new protocols for boat launching, requiring all boats launching to participate in seal program to prevent the spread of invasive mussels. According to the release, all vessels wishing to launch at Lake Berryessa will be inspected. A red quarantine seal will be applied for 30 days, during which the vessel will not be permitted to launch.