Midway Atoll is a 2.4-square-mile atoll in the North Pacific Ocean. The largest island is Sand Island, which has housing and an airstrip. Immediately to the east of Sand Island across the narrow Brooks Channel is Eastern Island, which is uninhabited and has no facilities. Forming a rough, incomplete circle around the two main islands and creating Midway Lagoon is Spit Island, a narrow reef.
Midway Atoll forms part of the Northwest Hawaiian Islands Important Bird Area, designated as such by BirdLife International because of its seabirds and endemic landbirds. The atoll is a critical habitat in the central Pacific Ocean, and includes breeding habitat for 17 seabird species. A number of native species rely on the island, which is now home to 67–70 percent of the world's Laysan albatross population, and 34–39 percent of the global population of black-footed albatross. A very small number of the very rare short-tailed albatross also have been observed. Fewer than 2,200 individuals of this species are believed to exist due to excessive feather hunting in the late nineteenth century. In 2007–08, the U.S. Fish and Wildlife Service translocated 42 endangered Laysan ducks to the atoll as part of their efforts to conserve the species.
Over 250 different species of marine life are found in the 300,000 acres of lagoon and surrounding waters. The critically endangered Hawaiian monk seals raise their pups on the beaches, relying on the atoll's reef fish, squid, octopus and crustaceans. Green sea turtles, another threatened species, occasionally nest on the island. The first was found in 2006 on Spit Island and another in 2007 on Sand Island. A resident pod of 300 spinner dolphins live in the lagoons and nearshore waters.
A number of invasive exotics have been introduced; for example, ironwood trees from Australia were planted to act as windbreaks. Of the 200 species of plants on Midway, 75 percent are non-native. Recent efforts have focused on removing non-native plant species and re-planting native species.
Lead paint on the buildings posed an environmental hazard to the albatross population of the island. In 2018, a project to strip the paint was completed.