The only way to reach Boldt Island, as well as the other 1,800-plus islands in the St. Lawrence River, is by boat. And several boat companies offer tours.
Largest among them is Uncle Sam’s Boat Tours (315/482-2611, www.usboattours.com [1]), whose huge replica paddleboats dock at the eastern end of James Street. Uncle Sam’s features an hourly shuttle service to Boldt Castle [2] (adults $7, children 4–12 $4.50) that allows visitors to stay as long as they like, as well as various sightseeing and dining cruises.
Empire Boat Tours (4 Church St., 315/482-8687, adults $6, children $3) also travels to Boldt Island and offer various sightseeing and dining cruises.
If you’d prefer to rent your own motorboat or pontoon boat, stop in at O’Briens U-Drive (51 Walton St., 315/482-9548). Rentals are available by the hour, day, or week, and river maps and trip-planning advice are provided.
Links:
[1] http://www.usboattours.com
[2] http://www.moon.com/destinations/new-york-state/the-adirondacks/the-thousand-islands/alexandria-bay/boldt-castle