There are some 3,820 lakes in New Zealand with a surface area larger than one hectare. Much of the higher country in the South Island was covered by ice during the glacial periods of the last two million years. Advancing glaciers eroded large steep-sided valleys, and often carried piles of moraine (rocks and soil) that acted as natural dams. When the glaciers retreated, they left basins that are now filled by lakes. The level of most glacial lakes in the upper parts of the Waitaki and Clutha / Mata-Au rivers are controlled for electricity generation. Hydroelectric reservoirs are common in South Canterbury and Central Otago, the largest of which is Lake Benmore, on the Waitaki River.
There are some 3,820 lakes in New Zealand with a surface area larger than one hectare. Much of the higher country in the South Island was covered by ice during the glacial periods of the last two million years. Advancing glaciers eroded large steep-side,d valleys, and often carried piles of moraine (rocks and soil) that acted as natural dams. When the glaciers retreated, they left basins that are now filled by lakes. The level of most glacial lakes in the upper parts of the Waitaki and Clutha / Mata-Au rivers are controlled for electricity generation. Hydroelectric reservoirs are common in South Canterbury and Central Otago the largest of which is Lake Benmore, on the Waitaki River.