So what was I doing in the drain last week? I had been told that a rare plant had been sighted somewhere on the Fowlmead site so I dutifully went searching.
The plant is Grass-poly Lythrum hyssopifolia, which was last recorded in Kent in 1913 and was down to just one small area in Cambridgeshire until recently - coincidentally the area was by the similarly-named Fowlmere, the RSPB reserve. It was worth a look, then. But being a maximum of six inches tall with tiny flowers, the chances were pretty slim.
It previously grew in muddy circular hollows in fields that dried out in summer, charmingly called pingoes. These were another victim of modern agricultural improvements, and the plant died out with the habitat. Where to look, on the large coal tip? I saw a dry ditch and started to walk along it.
And there, in a small area of bare mud, were about 110 small plants that matched the description. Photos were duly taken, and sent to the county recorder who of course wanted more details to distinguish it from False Grass-poly (what? I had hardly heard of the real Grass-poly).
So off I went again, but it had rained overnight and the dry ditch was inundated. I have observed the experts studying tiny plants with magnifying glasses, their noses pressed to the earth, but this was not going to happen here - you'd drown in two inches of water.
But today the water had flowed away, and there are still a few plants in flower, so better pictures are taken and the details checked. When the plant was first mentioned I recalled reading about it in Peter Marren's Rare Flowers book, and he gives a good account of the attempts to recover the species from the brink of extinction. If I may paraphrase it, in 1977 it "seemed to be one of the rarest and most endangered British plants.... It may have survived, largely unnoticed" at the Cambridgeshire site for 300 years since John Ray recorded it.
But then it started turning up at other sites, in Oxfordshire, West Sussex and Jersey. And then it was found at Slimbridge, where it has spread successfully by the wildfowl areas, and there are now "a total of 700,000 plants, admittedly most of them by a single pond, placing it among the numerically less rare species in the Red Data Book".
A scientific report is in the Journal of Ecology.
Presumably the seeds arrived at Slimbridge on the feet of geese or swans, but I wonder if we'll ever know how Fowlmead got its plants. My congratulations to the knowledgeable and sharp-eyed lady who saw it here.