They readily swim to island campsites. They adapt their lifestyles to the availability of food, often becoming nocturnal to avoid confrontations with us rather than sleeping at night like they usually do. Black bears can swim to island campsites. The best way to prevent food pilfering in bear country is to avoid the bears. That means by-passing campsites with bear tracks, fecal droppings, and scattered garbage.
Bears are regular visitors there.
But if you must camp at such sites, keep a clean camp. The less food odor in your camp the less chance the bears will linger when they make their rounds. Wash dishes immediately and dump the water away from the camp. Completely burn any edible garbage, including grease, rather than burying it or throwing it in a latrine. Most black bears will not enter a tent with people in it, but it is still a good idea to keep food and food odors out of tents and sleeping bags.