The first step is to identify each island. Looking on a map reveals that each island has an island pair, also hinted by the puzzle image, where two islands are separated by a body of water. The fact that numbers lie within the water and the title, straight across, hint at the next step - identifying the strait or body of water separating the island pairs. Indexing the numbers into the names of the bodies of water gives HECATE, the name of a strait in British Columbia, and the solution to this puzzle.

This stumper was far too unreasonable for new puzzlers given such a short hunt (1 hour), but I wanted to include at least one "serious" puzzle if any team cruised through other puzzles. Unfortunately, no one solved this puzzle, but overall I was pretty happy with the difficulty of the hunt and with the progress of teams. Next time, I will try and make it so every team solves at least one puzzle!