The longest river, Юjуrsб in the south, is 230 km long and has an average discharge of 390 cubic metres per second.
The second longest, Jцkulsб б Fjцllum in the northeast, is 206 km long. Other big rivers are Hvнtб and Цlfusб in the south, Skjбlfandafljуt in the north, Lagarfljуt and Jцkulsб б Brъ in the east.
Icelandic rivers are chiefly of two types, glacial and clear-water rivers. The former usually divide into numerous more or less intertwined tributaries that constantly change their course and swing over the outwashed plains lying below the glaciers.
This is especially true of the rivers running south from Vatnajцkull. In this area it was extremely difficult to build a permanent road, since the bridges and parts of the roads were constantly being washed away when the glacial rivers reached their maximum discharge, usually in July and August.
Clear-water rivers are of two kinds. One drains the old basalt areas and has a variable discharge with maximum flow in late spring. The other kind drains regions covered with post-glacial lava and usually has small variations in discharge, which makes them ideally suited for hydro-electric power production.
Waterfalls are an impressive characteristic of the youthful Icelandic landscape, and among the most famous are Gullfoss in Hvнtб, Dettifoss in Jцkulsб б Fjцllum, Aldeyjarfoss and Goрafoss in Skjбlfandafljуt, Hraunfossar in Hvнtб in Borgarfjцrрur and Skуgafoss in Skуgб.
Lakes in Iceland are abundant, but most of them are rather small. Some of these lakes are formed by subsidence, others fill glacier-eroded basins, still others are lava-dammed, while a few are ice-dammed.
The five biggest lakes in Iceland are Юingvallavatn (83 sq. km), which is 114 m deep, Юуrisvatn (70 sq. km), Lцgurinn (52 sq. km), the lagoon lake Hуp (45 sq. km), and Mэvatn (38 sq. km). Lake Mэvatn is world renowned for its fascinating scenery and incredibly rich bird life.
Icelandic rivers abound with salmon, while trout and char are plentiful in lakes and streams.
Two other species of freshwater fish are also to be found, the eel and the three-spined stickleback. None of these five species are really freshwater fish, but represent marine species that are establishing themselves in fresh water.