How do I buy a boat launch permit?

Boat Launch Permit Information: 

Buy an annual pass to launch at McKinley Marina, Riverfront launch, Bender Park, and South Shore Park during the Official Boating Season, May through October. Single-day passes can be purchased at onsite pay stations at each boat launch.

When available, you may also purchase your permit online here: https://county.milwaukee.gov/EN/Parks/Plan/Get-a-Permit