It seems I was right about the timber yard being 'vole-scaped'. As I arrived last night, a vole was busy weaving in and out of the rubbish, and I thought to myself that there must be more than one animal there to make such an impression on the banks. Because not only are there burrows, but at the point where the bank meets the water there's a kind of shelf so the voles can run along without being seen from above. Only fairly heavy and established mammal-traffic would produce that.
Later I walked a few hundred yards upstream to the swimming baths and spotted a water vole on the bank. It's hard to photograph them clearly on this stretch as there's a lot of vegetation, but I did manage to get a picture that was sharp enough to show me this animal had a damaged eye. Eye problems are very common in water voles and are often the result of fighting. In fact, two years ago I followed the fortunes of an Edgeley Road vole which had lost its eye entirely, but had survived the winter. Moreover, this vole was around till the summer and went on to bring up a family. So even though you'd think a lack of peripheral vision would be fatal for an animal at the bottom of the food chain, it doesn't necessarily spell disaster.
Anyway, I lost track of the vole at the swimming baths, but then thought I'd found it and zoomed in again. It was only when I checked the photos later I could see this vole's eyes were perfectly normal. So last night's vole total was three!