 I'm on the banks of the River Wye. I'm just downstream of Hereford at a place called Hom Lacey. I went canoeing along exactly this stretch of river a few years ago, and I can vouch for it. It really was gorgeous, clear, fast-flowing, teeming with life. But not today. It's murky, tea brown. Every stone at the river's edge is deeply furred over with a coat of sludgy green algae.