Hang spring-cleaning! I said this before I set off, because everyone knows it's the best thing to say if you want to meet a water rat. This is the centenary year of The Wind in the Willows, and those, should you need to know, were Moley's words on setting off on the journey that took him to Ratty's place on the riverside. O my! O my!

But Ratty, that is to say the water vole, has been having a hard time over the past century. A survey just under 20 years back showed that water voles had vanished from 67 per cent of their known sites: a pretty drastic decline. Since then they have been adopted under the Government's biodiversity action plan, and it is the job of organisations like the Suffolk Wildlife Trust to convert money into voles.

Penny Hemphill has spent five years looking after Ratty: and as a result, the Suffolk population has at least doubled. Which isn't bad, really. The problems are habitat destruction and fragmentation, pollution and mink: Penny has been at the sharp end of reversing these devastating things.

Which brought me to a small slice of heaven, and little house about half the size of a phone box. Into this I inserted myself and set about waiting. This was a beautiful bit of country, on private land, beautifully managed by Nick Oliver, a farming man besotted by wildlife.

Willow warblers sang all around, which was perfection enough to be going on with. Blackcap, chiffchaff and grasshopper warbler joined in: songs of deep, springtime perfection, redolent of lushness. I looked out on to a stretch of water fed by the River Box and prepared myself to wait.

There is always a slightly fraught thing about sitting in a hide waiting for a single species. You have to tune your mind in and resolve to enjoy everything else. Watching wildlife requires a sort of Zen-related mental trick: you have to combine high hopes with low expectations. So I had a listen to the willow warblers and gazed at the mayflies that dipped into the water, apparently water-skiing, leaving a remarkably strong bow wave behind them: females laying eggs, I later discovered.

But I was there to meet Ratty: and Ratty most generously appeared. A water vole looks like rat that has been transfigured (in Professor McGonagall's class, presumably) into a teddy bear, but got stuck halfway. The face is round and fat and charming: even Winston Smith would be perfectly happy surrounded by water voles.

Popping out, popping back: and then, finally, the ultimate revelation of self, for Ratty's soul is in water. A neat little plunge, a seamless transition for a beast that is equally adept on land and under the water, dry and wet through, wriggling nonchalantly but decisively below the surface, gleaming silver from the air-bubbles in his fur.

There is a strong human pull towards some creatures. Few people can set eyes on a snoozing pride of lions without wishing to curl up voluptuously among them, and I don't think it's possible to see a water vole without wanting to scoop him out of the water and make much of him. As champagne goes straight to the pleasure centres, so the sight of these little creatures goes straight to the endearment centres of the brain.

A joy, then, to report that there are an awful lot more of them about than there were 20 years ago. Hang pollution, hang habitat destruction, hang mink. O my!

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