The atoll is 25 km long and nearly 10 km wide, with a lagoon area of 103 km² and a total area including reef flat of 163 km². A channel leads into the lagoon from near the middle of the western side of the reef. Immediately south of the channel is Round Rock, which dries. The lagoon has about 85 patch and pinnacle Reefs. When the tide is falling, the water flows out of the lagoon and over the reef in all directions until the reef is uncovered, and then flows out through the channel on the western side. On the rising tide, a reverse effect is noted. Only few parts of the reef completely dry. Helen Island Helen island was discovered by the Spanish naval officer Felipe Tompson in 1773, who charted it as San Felix shoal. The only island of the reef, it is located near its northern tip. It is tiny in comparison to Helen Reef, about 20 to 40 m wide and 400 m long, or about 0.03 km² of land area. The densely wooded island sits atop a sand dune, which is 0.25 km² in extent and which is moving southeast, falling into the lagoon, at a rate 3 to 4 m per year. The island is uninhabited except for a marine ranger station of Hatohobei State, which was established in the early 1990s on the eastern side of the island, to guard the reef against foreign poachers. The station is permanently occupied by a staff of three. The island has been designated an Important Bird Area (IBA) by BirdLife International because it supports a breeding colony of black noddies, with some 25,000 birds estimated in 2004. There are also nesting populations of sooty and greater crested terns. Transit Reef 50 km east of Helen Reef is Transit Reef (Pieraurou), which appears on some maps and which is referenced as an island in the Hatohobei State constitution and constitutes the southernmost feature of Palau. Its existence as island, however, is doubtful, as it is not listed in the current Sailing Directions. The literal translation of its Tobian name Pieraurou is "Sandy Navigation Point", referring to a submerged sand bar rather than a reef or island. Traditional villages There is little information available on traditional village patterns in the Southwest Islands. Osborne noted several individual old dwelling places and one concentration of platforms and pathways. There