A typical midsummer Saturday, and the park was full of people, so there was little unusual to see in the way of bird life. There is a second blond Greylag Goose on the lake, darker than the one that arrived earlier this year.

And here is one of the young Grey Herons gazing pensively across the lake, almost certainly thinking of its next meal.

There was more interest under water. Nigel Reeve had seen my report of 12 May about the return of the crayfish after they had been wiped out in 2008 by an accident when workmen cleaning the Diana fountain released poisonous chemicals into the lake. And he had asked me to get a picture of one of the new crayfish, if possible.

The original ones in the lake were Turkish Crayfish (Astacus leptodactylus), and he thought that the new ones might be American Signal Crayfish (Pacifastacus leniusculus), which have become a pest species in Britain over the past few decades. Neither is native, of course, and they are none too welcome as they predate the larvae of native fish. It was noticeable that after the poisoning incident there was a brief boom in the number of fish in the lake.

The boss of the boat hire firm Bluebird Boats, Peter Scott, had told me that his workers had found lots of large crayfish in the lake. I happened to meet him on my way round the lake, and asked him if, the next time he found one, he could photograph it to determine its species. But he very kindly offered to find me one there and then, and sent me out with two of his men in a motor boat to bring one up.

Before 2008, there was a man who set crayfish traps in the lake, quite unofficially, and sold his catch to local restaurants. Now it seems that someone has resumed the trade. There were two crayfish traps in the shallow water between the boathouses, and after we had found them -- with some difficulty because the algae hid everything -- we retrieved two crayfish, one of which was very large, more like a junior lobster.

I thought this must be a Signal Crayfish because of its huge size and massive right claw. But when I got home and looked it up on the web, I changed my mind. Unlike a Signal Crayfish, it doesn't have any trace of red on its body, and it looks just like the Turkish crayfish shown here. So maybe a few survived in 2008, and have gradually bred up to large numbers again. Here is a close-up of the same creature.