Lara Maiklem has spent over 15 years on the banks of the River Thames in London, kneeling in the mud on the foreshore and staring for hours at a time at the same small patch of land. Maiklem is a mudlark: She looks for old objects—pins, buttons, clay pipe stems—that have been discarded in the river by long-forgotten ordinary Londoners. Unlike most rivers that run through cities, the Thames’ tidal rise and fall mean it’s constantly turning up new treasures. Maiklem’s Sunday Times bestselling book about her hobby, Mudlarking (Mudlark in the US), is a hybrid of history, memoir and nature writing.

What drew you to mudlarking?
I grew up on a farm and spent an awful lot of time on my own, wandering across fields and playing in the hedgerows. It taught me to enjoy my own company: If ...