How deep should a garden pond be?

Aim for a deep zone of 60–90 cm (2–3 ft) in cold climates so water does not freeze solid, with shallow shelves of 10–20 cm for marginal plants. In warm climates, 45–60 cm is enough.

Where is the best place for a pond?

A level spot with 4–6 hours of sun, away from large overhanging trees and underground cables or pipes. Shelter from strong wind and a view from the house are also helpful.

How do I keep pond water clear?

Balance is the key: plant oxygenators and floating plants to cover about half the surface, avoid overfeeding fish, remove debris, and use a small pump and filter if you keep many fish.

Do ponds need permission or fences?

Rules vary. Many places require pool or pond fencing when young children have access, and some require permits for larger excavations. Check your local regulations before digging.

Pond and Water Garden Basics

A pond is the most exciting thing you can add to a garden. Within weeks of filling it, dragonflies hover over the surface, birds drink and bathe, frogs and newts move in and the whole garden feels more alive. It is also less work than most people fear, once the first season of establishment is complete and the balance of plants and water settles.

This guide takes you through planning, building and maintaining a pond or water garden. It forms part of the Water Features & Lighting pillar, and smaller options are in Water Features for Small Gardens. Electrical aspects are covered in Outdoor Electrical Safety.

Wildlife pond or ornamental pond?

Wildlife pond: gentle slopes, native plants, no fish, little or no filtration. Low maintenance and rich in life.
Ornamental pond: formal shapes, clear water, perhaps fish and a pump with filter. Needs more care but is dramatic.
Mixed: a naturalistic pond with a few fish and a small pump is a good compromise.

Choosing the site

4–6 hours of sun keeps plants healthy without encouraging algae.
Away from big trees to limit leaf fall and root damage.
Level ground, so the edge does not show a water line on one side.
Check for cables and pipes before digging (call utility locate services).
Close to a power point if you plan a pump, filter or lighting.
Visible from the house or seating area.

Liner or preformed pond?

Option	Pros	Cons
Flexible liner (butyl/EPDM)	Any shape and depth; durable (20–30 years)	More effort to dig and shape; needs underlay
Preformed rigid pond	Quick to install; shelves already formed	Limited shapes and sizes; hard to level
Clay-lined (puddled)	Natural, for large wildlife ponds	Requires suitable clay and skill
Raised pool in timber or brick	No digging; formal look; child-friendly height	More construction; freezing concerns

For most gardens, a butyl or EPDM liner gives the best results. Avoid cheap PVC, which hardens and cracks in sunlight.

Step-by-step construction

Mark the outline with a hose or rope and view it from the house and seating.
Dig in zones. Start with a shelf 20–30 cm wide and about 20 cm deep around the edge (for marginal plants), then a deeper centre of 60–90 cm. Slope the sides at about 20° so wildlife can climb out.
Level the rim with a straight board and spirit level. A rim that is out by 2 cm will show after filling.
Remove sharp stones and lay 5 cm of damp sand or a geotextile underlay on the base and sides.
Lay the liner, allowing a generous overlap, and fill slowly with water while smoothing folds.
Trim and hide the edges with flat stones, turf or planting; tuck the liner under paving and make sure no liner acts as a wick to drain the pond.
Add plants and wait. Let water settle for several days. Avoid adding fish until plants are established.

Plants: the real filter

Plant group	Role	Examples
Oxygenators (submerged)	Oxygenate and compete with algae for nutrients	Hornwort, water crowfoot, curled pondweed (check local invasive lists)
Deep-water plants	Shade the surface, flowers	Water lilies (Nymphaea), water hawthorn
Floating plants	Shade and absorb nutrients	Frogbit, water lettuce (tender)
Marginals (shallow shelf)	Soften edges, wildlife cover	Marsh marigold, iris, water mint, pickerel weed, rushes
Bog plants (surrounding)	Transition to garden	Primula, astilbe, ligularia, ferns

As a guide, aim for about 50% of the surface covered by leaves in summer, and one bunch of oxygenators per 0.1 m² of surface. Use aquatic compost or heavy loam in baskets, topped with gravel, never ordinary potting compost, which releases nutrients that fuel algae. Avoid invasive aquatic species such as parrot’s feather and water fern; they are banned in many regions.

Fish and wildlife

Fish are optional. A wildlife pond is better without them; fish eat tadpoles and insects.
For ornamental ponds, stock lightly, about 2.5 cm (1 inch) of fish per 25 litres (6–7 gallons) of water, and add them after plants are established.
Feed sparingly; uneaten food rots and feeds algae.
Provide ramps, stones and shallow edges for hedgehogs, birds and frogs to get out safely.

Pumps, filters and lighting

A pump circulates water, powers fountains and waterfalls and feeds a filter. For a pond with fish, circulate the pond volume about once every two hours. Choose a pump with a pre-filter and clean it regularly. Add low-voltage LED lights beneath or beside the water for night-time sparkle (see Garden Lighting Design), and connect everything through an RCD/GFCI.

Maintenance through the year

Spring: clear debris, restart pump and filter, divide overgrown plants and add new ones.
Summer: top up with rainwater, thin excess plants and net out blanketweed (string algae) by twirling it around a stick.
Autumn: net fallen leaves, cut back dead foliage and cover the pond with netting if trees overhang.
Winter: keep a small area ice-free (a floating ball or pond heater) so gases can escape; never smash ice.

Pitfalls to watch for

Digging too shallow, so the pond overheats or freezes solid
Building under a tree, then fighting leaf litter forever
Putting in too many fish too soon
Using ordinary garden soil or fertiliser in plant baskets
Letting the pond edge be higher on one side than the other
Ignoring safety around children

Shortcuts worth knowing

Fill with rainwater when possible; tap water contains nutrients and chlorine that can cause algae.
Be patient with green water in the first months; it usually clears itself as plants establish.
Photograph the pond monthly. It is a great record of wildlife and plant growth.

Continue with these guides

Plan the planting around it with Creating a Moon Garden and Flowers That Attract Pollinators, protect against hazards with Outdoor Electrical Safety, and return to Water Features & Lighting.