A riverside walk to a great pub: the John O’Gaunt Inn, Hampshire

The limpid waters of the River Test link a stroll over chalk hills to a pub serving fine rustic roasts

Rivers are marked in blue on maps, but close up, they often disappoint, their water an opaque mud-brown. But chalk streams look like rivers in a child’s picture book, sparkling and shallow, with gravel beds and lush water weed bathed in sunlight shining through limpid water.

They owe their resemblance to a stiff G&T to permeable chalk bedrock that lets rainwater drain away without washing mud or silt into the waterways. The world has about 210 chalk streams, and 76% of them are in England, where they are compared to the rainforests or Great Barrier Reef, so rare is the habitat they offer. And like those ecological treasures, chalk streams are in crisis too – threatened mainly by water companies abstracting from them too greedily.