离开了主河道，他们进入了一个乍一看像是一个内陆湖的地方。
Leaving the main stream, they now passed into what seemed at first sight like a little land-locked lake.
地表河与地下河相连接构成长江主河道。
The main watercourse of Yangtze was made of some surface river sectors and underground rivers.
最后他们划离主河道转入一条与大河交汇的小支流。
At last they turned off the big river into a little side river that came down to join it.
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