From Legends of Le Détroit:
The missionaries, indignant at this exhibition of idolatry, broke the statue in a thousand pieces and in its place erected a cross, at whose foot they affixed the coat of arms of France with this:
Taking the largest fragment of the broken idol the missionaries...towed it to the deepest part of the river so that it should be heard of no more. But the tradition says that after the fathers were far away a band of Indians coming to offer their homage to the deity found only its mutilated remains. Each took a fragment which he placed in his canoe as a fetish and it guided them to where the Spirit of the Manitou had taken refuge under the deep sombre shadow of Belle Isle.
He bade them bring every fragment of his broken image and to strew them on the banks of his abode. They obeyed his order and behold each stone was converted into a rattlesnake, which should be as a sentinel... .
The Tugboat Hunter blog has a post with a view of the river from Belle Isle.