The Mute Swans nesting on the Serpentine island have brought their new brood out on to the water. There are five cygnets. This makes three broods of cygnets so far, totalling at least 14 -- it is still not clear how many there are at the outflow of the Serpentine.

There is probably a Great Crested Grebes' nest in the reeds at the south side of the outflow, but it is impossible to see anything except the parents going in and out. The bottom of the netting fence only reaches just below the water, so they can dive under it easily. It makes a useful barrier against predatory gulls.

There were still a few Swifts high over the lake, and some House Martins circling above the Kuwaiti embassy.

There is a thick growth of hair algae, especially on the Long Water, and likely to be a lot more if the hot weather continues. The algae started growing before the weather warmed up -- in fact in chilly weather that would not normally have started it -- almost certainly because the recent heavy rain caused a lot of soil to be carried into the water, bringing with it of nitrates and phosphates to feed the algae. The problem is particularly severe on the west side of the Vista, where the land drains overflow whenever it rains hard and a stream runs over the tarmac. It is exacerbated by the gardeners spreading leafmould on the grass. The amount of organic material going into the lake will have completely swamped any effect of the tons of expensive gloop they poured into the lake to absorb phosphates (if indeed this stuff has any effect). But on 18 May, just as the algae were beginning to thicken, there they were again idiotically spreading leafmould on the Vista to make the problem worse.

However, the algae are good news for some.

The Mistle Thrushes nesting near the Serpentine Gallery were hopping around the grass, standing stiffly upright when they stopped.