Mary Island State Marine Park
Boat-Access-Only Island Camping on the St. Lawrence River — Thousand Islands Region of Northern New York, Primitive Camping Sites on a Rocky Island in the Legendary St. Lawrence River, Accessible Only by Private Boat (No Ferry Service Available), Fishing for Largemouth Bass Smallmouth Bass Northern Pike and Muskellunge in One of the Best Freshwater Fisheries in the Northeastern United States, Spectacular Thousand Islands Scenery With Views of Islands, Channels, and Passing Freighters, Swimming Off Rocky Island Shoreline, Nature Trails Through Island Forest, Part of the Thousand Islands State Park System, Near Clayton and Alexandria Bay Jefferson County Northern New York
Mary Island State Park is a boat-access-only state park on a rocky island in the St. Lawrence River in the Thousand Islands region of Jefferson County, northern New York, managed by New York State Office of Parks, Recreation and Historic Preservation. The park features primitive camping sites on the island accessible only by private boat (no ferry service), fishing for largemouth bass, smallmouth bass, northern pike, and muskellunge in the legendary St. Lawrence River — widely considered one of the best freshwater fisheries in the northeastern United States, swimming off the rocky island shoreline with crystal-clear river water, nature trails through the island’s mixed forest, spectacular Thousand Islands scenery with views of dozens of islands, river channels, and passing international freighters, and a remote, peaceful atmosphere that exemplifies the Thousand Islands island camping experience.
The Thousand Islands region of the St. Lawrence River is legendary among bass anglers — the clear, rocky waters around Mary Island produce trophy-class smallmouth bass that draw competitive anglers from across the Northeast and Canada. The muskellunge (musky) fishing in the St. Lawrence is also world-class.
Mary Island provides a true island camping experience in one of America’s most scenic river systems — arrive by boat, set up camp, and enjoy the spectacular river views, passing ships, and complete solitude that only an island can provide. The Thousand Islands are also famous for Boldt Castle and historic river mansions visible from the water.
Things to Do
- Island camping — primitive, boat-access only
- Fishing — bass, pike, musky (world-class)
- Swimming — crystal-clear river, rocky shore
- Boating — Thousand Islands channels
- Nature trails — island forest
- Sightseeing — islands, freighters, Boldt Castle
Park Information
| Feature | Details |
|---|---|
| Location | St. Lawrence River, Thousand Islands, NY |
| Access | ⚠️ Boat-access ONLY — no ferry |
| Camping | Primitive island sites |
| Fishing | Bass, pike, musky (world-class) |
| Nearby | Clayton, Alexandria Bay, Boldt Castle |
| Managed By | NY State Parks |
| Coordinates | 44.3167° N, 75.9500° W |
Frequently Asked Questions
Wildlife & Nature
Mary Island State Marine Park — on the St. Lawrence River in the Thousand Islands — provides an island accessible by boat. The island’s forest and rocky shoreline offer primitive camping and fishing. Bald eagles nest nearby. Great blue herons fish the channels. Smallmouth bass and northern pike provide excellent fishing.
Nearby Attractions
Thousand Islands — surrounding. Alexandria Bay — nearby — has Boldt Castle. Clayton — nearby — has the Antique Boat Museum.
How do you get to Mary Island State Park?
Mary Island State Park is accessible only by private boat — there is no ferry service to the island. Located in the Thousand Islands region of the St. Lawrence River in Jefferson County, northern New York, the park offers primitive island camping with world-class fishing for smallmouth bass, largemouth bass, northern pike, and muskellunge. Swimming off rocky shoreline in crystal-clear river water, nature trails through island forest, and spectacular views of the Thousand Islands, passing freighters, and nearby Boldt Castle. Part of the NY State Parks Thousand Islands system.
Last updated: May 2026
