At dawn the first adult midges start to break out. Soon, millions upon millions of newly hatched lake flies are taking to the wing. Early explorers told tales of lakes that smoked, as if on fire. But these spiralling columns hundreds of metres high are mating flies. Once the flies have mated, they will all drop to the water surface, release their eggs and die. Malawi may look like an inland sea, but it's dwarfed by the world's largest lake - Baikal in Eastern Siberia. 400 miles long and over a mile deep, Baikal contains 1/5 of all the fresh water found in our planet's lakes and rivers. For five months of the year it's sealed by an ice sheet over a metre thick.


凌晨第一只成年摇蚊冲水而出。不久，亿万只刚孵化的摇蚊飞起来了。早期的探险者们说到，这些会冒烟，好像着了火一样。但是这些高达数百米的盘旋的烟柱实际上是正在交配的摇蚊。交配完毕之后它们会降落到湖面产卵，然后死去。马拉维湖看起来像一个内陆海，但比起世界上最大的湖，位于西伯利亚东部的贝加尔湖，它就相形见绌了。贝加尔湖长600多公里，深达1600多米，它的水量占地球全部河湖淡水总量的1/5.每年有5个月时间它都被厚达1米的冰层覆盖。