I’ve been building, not so much a garden pond, as a playground pond. And the first problem with playgrounds is that they are all-over tarmac. The obvious site for Ivydale Primary School’s new pond was a sunny, but extremely bleak corner next to the electricity sub-station building. Digging up the hard-standing was never a possibility: too much effort, too much time, too much money, too much noise, and too many pipes and cables running who knows where. So we opted for above-ground construction instead.

First, we laid out four sleepers in a square, then stacked the others on top like a game of giant Jenga. Simply screwed together at the corners, they sit in place quite happily. Next we piled in a cubic metre of gravel for drainage, and sat the fibreglass liner on top of it. The raised pond in our garden at home is a similar construction. Ours is triangular, so we had to borrow a chainsaw (it’s remarkable the number of people in south-east London who just happen to have a chainsaw). We used a butyl liner, but discovered our mistake when it sprung a leak (or was it punctured by small child with stick? We shall never know). At the school, toughness is all, so a robust, moulded fibreglass insert is perfect, and hopefully damage-proof, when it comes to pond dipping later in the year.

Next we filled in the area around the fibreglass with topsoil, logs, rocks and pot shards to give the pond edges texture, sheltering crevices and support. We landscaped the soil between the liner and sleeper frame, and filled the pond with water.

We’re not quite all the way there. The pond is full of water and has already taken on a deep green bloom as the algae and microbes start to establish an ecological balance, but the pond surround needs to be planted up and after the soil has settled we’ll need to back fill a bit more.

We’re going to have to put up a sign explaining that the pond will not have fish in it. It’s a wildlife pond, and in my book fish and wildlife do not mix. And it’s unlikely that frogs or toads will find their way across the barren and exposed playground tarmac to colonise it. It will be an invertebrate-friendly pond. It’s already home to some daphnia (water fleas) brought in with the water lilies and some water skaters that have flown in from some pond or other further down the road. It will not be long, though, before it is crawling with life.