At every box store that carries plants and supplies, you will see a display of preformed pond liners for your backyard pond. They come in all kinds of shapes from round to oval to irregular. Most of them are made of some sort of composite material that resembles a thick form of plastic.

Like anything, there are a number of pros and cons to using a preformed pond liner.

1. They mostly come in smaller sizes so you can create a pond for a small space with more ease than if you used a flexible liner.
2. You know immediately what shape your pond will be when you finish.
3. You can stack several in succession to create small waterfalls or longer, shallow ponds to fill a slightly larger area.
4. Since they are made of thick, solid material, they are less likely to spring a leak due to freezing and thawing or if you accidentally touch them with a sharp stone.
5. Overall, they can be a relatively inexpensive way to have a backyard pond.

1. You are limited to the forms, shapes and sizes of the pond liners that are available. This limits your creativity and options for design considerations in your landscape.
2. Unless you do a very good job of creating a foundation for the preformed pond liner, it may be pushed up and out of the ground with the normal freezing and thawing of the soil during winter. This may cause you to have to reset it every spring. Yuk!
3. Many preformed pond liners are only a foot or so in depth which is often not conducive to overwintering fish.
4. With a relatively small volume of water, you may experience more problems with algae unless you do a good job of filtering and frequent partial water changes especially if you put a few goldfish in for the summer.