Eastern Arch is an advanced Poor Knights wall-and-arch dive where a kelp-framed western entrance leads into steep sponge-coated walls and a more exposed blue-water exit on the outer side of the islands. The site is prized for dramatic structure rather than easy shelter. Divers usually work the line the skipper chooses for the day, watching for nudibranchs, moray eels, schooling fish, and passing rays as the arch opens toward the open ocean.