Yes, dogs on leashes are allowed on the Three Sisters Islands.

Yes, provided they’re leashed.

The Three Sisters Islands are part of Niagara Falls State Park (the New York side), and the park’s general rule is dogs must be on a leash no longer than six feet. They’re not allowed inside buildings or on the Cave of the Winds tour, but the islands themselves are fine. Bring water—there aren’t many drinking fountains for dogs—and be ready to dodge goose poop. Clean up after them; the park takes that seriously.

This is not a place to let them off-leash, even if they’re well-behaved. The currents around those islands are no joke.