What it is to be young, energetic and adventurous and to think nothing much of spending three months paddling down a 2,000-mile-long river through the Canadian and Alaskan wilderness to gather material for a book. Adam Weymouth’s account of his journey down the Yukon is truly an epic. It is to his credit, and to the benefit of this fine book, that he makes so little of the dangers and discomforts he endured.

There is the odd hairy moment: shooting rapids with the river ‘lunging, shaking, clawing at the raft’; a terrifying crossing at night in a storm to a village on the lower Yukon, with the waves crashing onto the canoe and Weymouth and his Swedish girlfriend paddling and bailing like demons. And there was obviously a great deal of monotonous and wearying grind, often in relentless rain, when the water flowed slowly and the banks were often two or three miles apart.

But in some ways braver still than choosing to subject himself to such an ordeal was Weymouth’s decision to focus his narrative on a particular fish – a distinctly tricky thing with which to engage the reading public’s attention. Admittedly the fish in question, known as the king