No one knows why a salmon takes a fly. The feathered hooks that bob in Highland rivers are not seen as food to the marathon travelling fish because salmon don’t feed in freshwater. Yet something about these flies draws them inexorably towards their death, and it’s impossible to say what that is. As one talking head comments in Kiss The Water, he doesn’t want to ever find out why.

It’s this approach of portraying salmon fishing as something magical, of possessing some ineffable mysticism about it, that makes this documentary so special. Ostensibly about Megan Boyd, a craftswoman who was so good at making salmon flies she was given an MBE for it, it somehow becomes a moving examination of craftsmanship, of Highland life and the importance of tradition. The film goes into great detail about why her flies were so brilliant, exploring the history behind the process, and it shows us close-up sequences of these flies being made. They are undoubtedly beautiful works of art and also essential tools for the keen angler.

Yet there is more to the documentary than an examination of this particularly niche trade. Boyd sounds like a fascinating person, but she died in 2001 so she doesn’t appear in the film, even in archive footage, and her craft is now declining. The result is a film that is an elegy to Boyd, to salmon flies, to fishing and to Scotland. Director Eric Steel collects anecdotes about her, and soon it emerges that her intricate designs embraced all levels of society, from local village boys in Brora, Sutherland, to Prince Charles himself, who received a personalised design on the day he married Diana. It’s as much about how Boyd is remembered as it is about Boyd herself.

Clearly, her art reached hundreds and thousands of lives, and the anecdotal presentation of these recollections portrays her as an almost mythic figure, whose flies provided record breaking catches from rookie anglers. The anecdotes themselves are delivered with the gentle warmth of people who knew her, although one suspects that no one would claim to have truly known her well. Steel’s decision to cut these stories with gorgeous shots of Scottish scenery and repeated images of moving water makes the memories feel even more ephemeral, and slowly paints a portrait of Boyd as a woman who was and became a part of Scotland. The documentary therefore takes on far wider significance beyond a single life, and becomes a nostalgic look at tradition and seclusion.

Weaved throughout these memories of Boyd and fishing are a series of animated interludes that represent the themes and events described in the film in an abstract way. These stunning, painterly sequences, combined with an occasionally overbearing but moving score, add another layer to a documentary that takes one life of simplicity and creativity and turns it into something with a deep emotional resonance. No one knows why a salmon takes a fly, but in Eric Steel’s gorgeous documentary, the ‘why’ suddenly becomes unimportant.

Kiss The Water is playing at Edinburgh International Film Festival on 23 & 24 June