Washington State’s requirements are listed on the home page +
In addition, all aircraft using WA waters must purchase the WA AIS permit for seaplanes. On the Washington Department of Fish and Wildlife website link below, go to "Product Categories > Other” to select the Seaplane Permit.
If you need to have the state decontaminate your aircraft, you can call 360-902-2200 option 2 for enforcement to request inspectors to schedule a place and time to meet you.
OREGON has approved the training and requirements listed on the home page
MONTANA has approved the training and requirements listed on the home page, however . . .