[4] His environmental novel The Stream (2000)[5][6][7] was described by David Arnold-Forster, chief executive of English Nature, as "the most significant book of its kind that I have read since Rachel Carson's Silent Spring".
His lifelong interest in angling began with sticklebacks and minnows on the River Skerne as a child, then moved on to coarse fishing on the Tees and Swale.
The book recorded the experiments Clarke and John Goddard conducted on the way the reflection and refraction of light influence the world as the trout sees it and involved much underwater photography.
[12] Although each is widely read in his own right, the names of Clarke and Goddard are permanently linked[13] through the book and through The Educated Trout (1980), a 50-minute film in the BBC Television series The World About Us that documented their researches.
[15] He was elected an Honorary Life Member of The Flyfishers' Club in 2005. Who's Who lists his non-angling interests as "walking, photography and sitting still in the countryside, watching and listening."