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At dawn, the first adult midges start to break out.
黎明时分，第一只成蚊破蛹而出
Soon, millions upon millions of newly-hatched lake flies are taking to the wing.
不久，成百上千万只新羽化的幽蚊全都扇动着翅膀飞到空中
Early explorers told tales of lakes that smoked as if on fire.
早期探险家看到这种湖面上“冒烟”的情景，还以为是湖底着了火
But these spiralling columns, hundreds of metres high, are mating flies.
这些高达数百米的螺旋型“烟”柱，其实是正在交配的幽蚊
0nce the flies have mated, they will all drop to the water surface, release their eggs and die.
幽蚊完成交配之后，便会一起落到水面，产下卵，然后死去
Malawi may look like an inland sea, but it's dwarfed by the world's largest lake.
马拉维湖看起来像大海一样辽阔，但它远比不上世界上最大的湖泊。
Baikal in eastern Siberia.
东西伯利亚的贝加尔湖
Four hundred miles long and over a mile deep,
贝加尔湖长400英里，深度超过1英里，
Baikal contains one-fifth of all the fresh water found in our planet's lakes and rivers.
其中的淡水储量占到了全球江河湖泊淡水总量的1/5
For five months of the year, it's sealed by an ice sheet over a metre thick.
每年中总有5个月，湖面被1米厚的冰层覆盖。
