Thames, London [Photo Source: huanqiu.com]

6. For hundred years, the Thames River is always the main stream of London. Since the early stage of Middle Ages, the London city started to expanding to the river bank, which makes the watercourse narrower and narrower. Until 1983, the local government built the Thames Barrier. The flood sweeping London every year has just been controlled. But facing the rising sea level, this could be not enough.