Most preformed ponds are sturdily made from HDPE (High Density Polyethelene), which is good news for the consumer as this is a heavy duty material with a long life span.
High Density Polyethelene
HDPE is very resistant to temperature change and UV rays, so will withstand winter as well as summer weather and will not deteriorate when exposed to sunshine.
Lotus Instant ponds are an excellent choice for beginners or if you have a restricted budget, and the same company also markets the larger, deeper, Toughline range.
Other well known names such as Blagdon, Oase and Bermuda all have an attractive range of ponds with capacities from a modest 150 to 1000 litres.
Fibre glass ponds such as those manufactured by Atlantis are also UV and frost resistant. Heavier than HDPE, they are extremely strong and covered by a lifetime guarantee.
Once you've made a decision on whether to go for HDPE or fibre glass, the pond's shape and size will depend on considerations such as the dimensions of your garden and what type of pond you desire in the sense of formality or natural shape.
Plants And Fish
One criticism of preformed ponds as opposed to butyl liners is that they look too formal. However there is now a tremendous choice available that accurately mimic real life ponds.
With aquatic plants placed in baskets on the shelves, a 'natural' look can be easily achieved and the pond will be quickly filled with wildlife.
The amount, depth and width of marginal shelves will dictate how many and what type of plants can be grown in the pond. If possible there should be shallow, marginal, and deep water to suit different species of plant, and inspiration can be gained from The Gardener blog 'How To Transform Your Pond with Plants'.
Also, the number and type of fish that can be kept depends on the pond's volume and, to enable fish to overwinter, the pond needs to be approximately 2ft (60cm) deep. With a pond of that depth evaporation won't be a problem during the summer and, in the winter, frozen water will only affect the surface.