It is the nature of estuaries to be deeply mysterious and very hard to know. Taking from both the river and the sea, they belong to neither. They form their own world in which fresh and salt water are forever churning. The dry land with its human settlements contains the estuary, but its essence is the endlessly moving water, the shifting sandbanks and mud banks, the channels, the tearing currents.

It follows that to tell the story of any estuary successfully requires a kind of spiritual immersion, the slow acquisition of knowledge derived from extended exposure and some kind of close identification. In the case of the Thames Estuary, geographically vast and historically rich to a phenomenal degree,