Also, because human societies have always made use of water, sometimes the remains of structures that these societies built underwater still exist (such as the foundations of crannogs,[9] bridges and harbours) when traces on dry land have been lost. As a result, underwater archaeological sites cover a vast range including: submerged indigenous sites and places where people once lived or visited that have been subsequently covered by water due to rising sea levels; wells, cenotes, wrecks (shipwrecks; aircraft); the remains of structures created in water (such as crannogs, bridges or harbours); other port-related structures; refuse or debris sites where people disposed of their waste, garbage and other items, such as ships, aircraft, munitions and machinery, by dumping into the water.