The St. Lawrence River begins at the Thousand Islands. There are actually 1,800 islands filling an area 15 miles wide at the Lake Ontario end, then tapering to 5 miles over a downstream distance of about 50 miles.

Because these islands were once mountain peaks, water depths between them can change abruptly from more than 50 feet to nothing.

The islands themselves range from tiny granite outcroppings to forested land large enough to support a village.