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How deep should my pond be?

A healthy garden pond will be around 46cms / 18 inches deep, while a successful koi pond, or pond with larger fish, a depth of at least 90cms / 3 feet is advised.

Why is pond depth important?

A pond that is too shallow is at risk of sudden extreme temperature fluctuations, getting too hot in the summer and too cold in the winter. These heat fluctuations could negatively impact fish health and cause rapid algae blooms in the summer.

A healthy and balanced garden pond will have plant shelves around the edge at varying depths, usually between 15 and 30 cms deep, for healthy marginal plant growth. The deepest area of the pond should be at least  40% of the pond area.

 Tips on Pond Depth

  • 90cm (3ft) or more for large fish.
  • 45cm (18in) or more for smaller fish.
  • At least 40% of the area at max. depth.
  • Deeper ponds have less temperature fluctuations, helping create a healthy environment.

TOP TIP: Pond depth is the actual water depth, not the excavation depth. Add at least 15cm (6 inches) to your excavation depth to allow for the difference in the top of the pond and the water level.

How deep should a koi pond be?

A depth of 91cms (3 feet) and 122cms (4 feet) is considered optimum for a healthy koi pond in the British climate. This depth will protect your koi from most of the temperature extremes the UK climate can throw at us while giving the koi a good volume of water to move around in. Remember, a deeper ponds water temperature will take a few days to adjust to any sudden changes in the ambient air temperature, which may affect your choice of foods and fish husbandry. 

How deep should a wildlife pond be?

Shallow ponds are great for wildlife – Unless you are keeping fish, the deepest areas need to be no more than 25-30 cm (1 foot) deep. This keeps all of the pond well oxygenated and well lit. It also means you can see to the bottom, helping you to enjoy your pond more. If you want a deeper pond, try to make sure its surface area is 5-10 times the maximum depth, otherwise there is a good chance you’ll suffer from deoxygenation problems.

How deep should a garden pond be?

A depth of 46cms (18 inches) is the minimum depth recommend to achieve a healthy pond balance. At least 40% of the pond area should be at the maximum depth, with the sloping edges stepped for marginal pond plants. Good pond planting will help your pond's ecosystem and offer shade, helping reduce algae blooms and sudden temperature fluctuations. Read our guides to pond plants and planting.

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