Environmental dangers include uncontrolled spread of the crown of thorns starfish, which flourishes in deepened channels and is destructive to coral reefs; erosion of beachheads from the use of sand for building materials; and excessive clearance of forest undergrowth for firewood. About 40% of Funafuti is uninhabitable because the United Kingdom authorized the US to dig an airstrip out of the coral bed during World War II. Global warming and the related rise of sea levels are also a significant environmental concern for Tuvalu's residents. The encroachment of sea water also poses a threat of contamination to the nation's limited water supply, whose purity is already at risk due to untreated sewage and the by-products of the mining industry and farming. Natural hazards include earthquakes, cyclones, and volcanic activity.
In 1986, the government approved the first phase of an EC-financed sea-wall system to protect the coast. Current fishing methods threaten Tuvalu's marine life. The green sea turtle, hawksbill turtle, bay shark, and the leatherback turtle are endangered.