Longer than most folks think. I snorkled all over the pacific rim and it's sad how much pollution is in the ocean...we've been killing the coral reefs for many decades. For the most part the beaches are clean...it's the water that's often not or the ocean floor..I think Hawaii has the cleanest water I've snorkeled in and it's the furthest from any major continents. In many poor countries you could pay any sailor with a raft to dump anything you want in the ocean for 50 bucks or so. I've seen medical waste bags covering coral reefs before.