One of the biggest disadvantages of a preformed pond liner is the relatively shallow design. Very few preformed liners, regardless of size or material, offer enough depth for supporting more than a few decorative fish. Water depth plays an important role in maintaining proper temperature, dissolved oxygen levels, and other quality parameters. Settling for a shallow design, just because it would allow you to use a preformed pond liner, is likely to interfere with your plans for the pond. Even small backyard ponds, added only for decoration, require more maintenance and repairs if they are too shallow.
Common Depth Limits
Most rigid, preformed pond liners that are constructed from plastic or fiberglass top are made to a maximum depth of 18 to 24 inches. Two feet of depth may sound reasonble, but the addition of any sand and rocks will quickly reduce that figure. The constant accumulation of natural muck from falling leaves and other debris also affects how much water depth is actually available. Koi generally thrive in ponds that are a minimum of three to four feet deep, and coldwater fish species like trout and bass often need a depth of 12 feet or more. Even custom formed, box-welded liners tend to offer a very limited depth. Flexible pond liners can be installed to practically any depth, letting you build a pond or lake as deep as you need it.
Advantages of a Deeper Pond
Some of the many advantages of increasing the depth of your pond include:
- Cooler temperatures that reduce weed and algae growth
- An appropriate environment for a wider range of fish species; especially if you consider heaters
- Reduced water loss; due to evaporation and wind spray
- More stable water quality parameters; like temperature and dissolved oxygen
- Resistance to drying out during droughts and summer weather
- Greater water holding capacity during a 100-year flooding event
- Less need to dredge and clean the pond of muck.
Fish Depth Requirements
Each species of fish commonly raised in backyard or commercial ponds requires a different set of conditions for optimal growth. However, many of them share similar depth preferences, allowing you to mix and match a few species with the right design. Preformed ponds are generally too shallow for almost all fish species; aside from goldfish and small koi. Koi can easily outgrow a two-foot pond in a few years, causing them to struggle to swim correctly and making it difficult for them to get enough oxygen. Starting with a pond that is at least three to four feet deep will allow you to adjust its use later, without having to remove the rigid liner and redo the excavation.
Space for Plants
Don’t assume that water plants want to live in shallow ponds either. While many marsh and edge plants can handle just having their roots covered with water, floating and fully submerged plants often need at least 16 to 18 inches of water to thrive. If you’re interested in growing water lilies, lotuses, or cat tails, you’ll want more depth than most preformed pond liners offer.
A shallow pond heats up and cools off faster, grows more algae, and requires more maintenance than a deeper one. While there’s also a maximum preferred depth for most uses, preformed pond liners don’t come anywhere close these measurements. Stick with flexible liners from BTL Liners, to create a pond with exactly as much depth as you need for fish, plants, or other uses.
