To the River: A Journey Beneath The Surface, By Olivia Laing

I am haunted by waters", Olivia Laing tells us, as in this book she joins the best nature writers, becoming part of the revival begun by Richard Mabey. With it comes an inclination towards rhetorical ornament that can become self-consciously obtrusive. But not here. Laing is a brilliant wordsmith and this is a beautifully accomplished book. It recounts a walk she made, in the course of one week, tracing the path of the River Ouse in Sussex. The catalyst was a "minor crisis". The loss of job and boyfriend in quick succession proved an immediate stimulus. But this walk also engaged the depths of what she knew, and preparation for it must have begun in childhood.

Laing is a superb naturalist. She can describe the architecture and ornamentation of pollen. She looks so sharply at wheat and at other things around her that at one point she travels no more than a few yards in one hour. She shares in the pleasures and irritations of a solitary walker, kicking her backpack irritably when a path takes her astray.

But like that great anatomist of melancholy, WG Sebald, she also allows the journey to trigger historical, literary and mythological reflections. Take the view over the meadows from Lewes Castle. This brings to mind the soldiers and horses who drowned as they fled during Simon de Montfort's challenge to Henry III at the Battle of Lewes in 1264. Here, too, tellingly encapsulated, is the tragic story of Kenneth Grahame's son, for whom The Wind in the Willows was written.

Laing's discursiveness is always entwined with her obsessive hydrophilia. But it is inevitable that the Ouse should be associated with the Woolfs: here Virginia committed suicide, as Leonard realised the moment he saw her stick lying on its bank. But none of Virginia Woolf's biographers has identified, as Laing does here, the watery start to their partnership.

"They went on a date to the Titanic inquest," she reminds us, also throwing in the first kiss by the English Channel and a boat trip up the Thames to Maidenhead. Wackily erudite on any subject she cares to make her own, Laing is equally canny on fossil hunting, and how it changed our view of the world, as she is on the strange machinations behind the Piltdown forgery.

"Water is sly; make no bones about it," she warns. There follows an absorbing account of the engineering involved, down the centuries, in the reclamation of marshes. It is preceded by a passage on floods, beginning with the biblical flood, taking in the St Elizabeth flood of 1422 and ending with that which severely damaged Lewes in 2009. "There's something about a flood, something mythic and disturbing, that gets to the heart of uncertainties about our place in the earth at all."

This note of ontological enquiry deepens as the book progresses. "How strangely we spend our lives," she remarks, after analysing the architecture of Hades, with the help of a map that will be familiar to readers of Dorothy Sayers's Penguin translation of Dante. Heaven, too, is reviewed, from various perspectives, while she also keeps Ithaca, Odysseus's destination, in mind. But it is finally the land that Laing loves best, that which is "planate with water, their histories conjoined", in which she places her faith. Sharing Woolf's observation of the Ouse valley – "this has holiness. This will go on after I am dead" – she finally rattles home in the train to Brighton.

Frances Spalding's 'John Piper, Myfanwy Piper: lives in art' is published by Oxford