Lake Vostok cross-section, cutaway artwork. This lake in Antarctica, the largest known subglacial lake in the region, has a surface area of around 14,000 square kilometres. Liquid water is thought to take thousands of years to pass through the lake (arrows). Ice cores have been taken (apparatus at upper centre) to a depth of several kilometres. Ice-penetrating radar and other studies have identified hundreds of lakes and shallow, swamp-like features below the Antarctic ice. It is thought that these environments form vast watersheds connected by rivers and streams that flow under the kilometres-thick ice sheet. When studying such ecosystems, care must be taken to avoid contamination.