Niihau or Niihau (; Hawaiian: ) is the westernmost and seventh largest of the inhabited Hawaiian Islands in the U.S. state of Hawaii, lying southwest of Kauai across the Kaulakahi Channel and having an area of . Several intermittent playa lakes provide wetland habitats for the Hawaiian coot, the black-winged stilt, and the Hawaiian duck. The island is designated as critical habitat for Brighamia insignis, an endemic and endangered species of Hawaiian lobelioid. The United States Census Bureau defines Niihau and the neighboring island and State Seabird Sanctuary of Lehua as Census Tract 410 of Kauai County, Hawaii. Its 2000 census population was 160; Its 2010 census population was 170.