Oh, for a pond as clear as gin

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On hot summer evenings, gardeners may dream of sparkling fountains tinkling into crystal-clear pools. All too often, though, the reality of a garden pond is a green- ish fetid puddle where fish gasp in a muddle of blanket weed and slime. Yet there are many solutions to most pond problems.

Clair Henley, of Wychwood Carp Farm in Hampshire, says the only essential is a water lily. Her family has 330 different kinds, the largest collection in the world, grown in 40ft-long ponds, with no pumps, no filters and no oxygenating plants. Water shrimps and water fleas are added to eat the algae, but tha's all. Her ponds are clear as gin, for some reason a favourite simile among water gardeners.

About pounds 50 would buy a flexible PVC liner, a few oxy-genating plants, a couple of small water lilies and some tiny fish. In theory this, plus an afternoon's digging and some paving or turf to hold the edges of the liner, is all you need for a pond about five feet by three. At first it will go green, but be patient, do not show it to lunch guests, many of whom will offer conflicting advice about how to deal with it, and in a month it will gradually clear.

With the right plants, such a pond should need little maintenance for several years. The water may need topping up occasionally and, in late spring, the lilies may need thinning.

Generally, a pond should be 18 inches deep, at least in the middle, to accommodate different plants. It should not be overhung with trees, as their leaves will drop and make the water murky. A third of the water surface should be covered with water plants such as lilies to keep some sun off the water. If you want fish, the pond must have oxygenating plants, that is, plants which grow submerged, like those in indoor fish tanks. They provide oxygen and compete with algae for nutrients.

The main pond problem is the algae - of which there are many different types, all bad. Microscopic single-celled plants give the water a greenish tinge, slime gathers around the edges and on rocks, and the dreaded blanket weed seemingly can fill a pond with fine hair- like strands in a few days.

If the combination of submerged plants and water lilies does not keep the pond clear, then algaecides can be used, but they may be only a short- term solution. It is more important to get the balance of plants right and to feed fish sparingly or not at all. Fish food is not all digested, which adds to the murk.

There may be other problems. If the pond becomes popular with frogs, you may need to find a home for masses of spawn, as a small pond will not support many tadpoles. Herons may be a hazard: trip wires will stop them from walking into the pond and eating the fish. And to protect small children, the whole thing may have to be covered in netting to stop them from falling in.

If you want to hear a merry tinkling, a reconstituted stone frog can squat beside the pond and spout water, although moving the pond's water around will not keep it clear. With small ponds, a real frog is better than a fountain as water lilies do not like their leaves splashed.

If this all appears to be rather low-key, then Mickfield Fish Centre in Suffolk will excavate and build a large pond, rock garden, waterfall and bog area, complete with pump, filtering system and a full complement of plants and fish for about pounds 5,000.

Or a visit to Christie's saleroom recently, for example, could have secured a 19th-century Italian white marble fountain with caryatids holding a fluted dish and surrounded by Bacchic rams; it sold for pounds 12,650. But that would be only the start, as it would need a pool to stand in, a filter and pump to operate it and plumber, electrician and stonemason to bring it all on-stream. And, presumably, a gin and tonic to drink beside it.

Wychwood Carp Farm, Farnham Road, Odiham, Hook, Hampshire

RG29 1HS.

Mickfield Fish Centre, Debenham Road, Mickfield, Stowmarket, Suffolk IP14 5LP.