There are quite a lot of things to think about when you decide to make a pond.
1) Wildlife or ornamental
2) Size and shape
3) Liner, preform or mud/clay
4) What to keep in it.
Lets start with deciding on a Wildlife or an ornamental pond or even to have a mixture of both. Most people would say that they cannot mix but I have had good success with having both a wildlife pond and then adding fish into the pond. Yes the fish do eat quite a few of the tadpoles and frogspawn, but a great many survive and when the frogs desert you for many months of the year the fish bring colour and life into the pond.
If you truly want just a wildlife pond bringing nature in, then you could have Sticklebacks or Minnows as your main fish (if you want any fish at all) and then whatever frogs, toads, newts and snails that find their way to your pond. You wouldn’t have to wait long before these lovely creatures find their new home with you or you could even find someone who would like to donate some from their pond to help you on your way. Maybe you would also decide not to have any filters or pumps and just use plants to clean and oxygenate the water. I think a wildlife pond would be informal. It would need some sloping sides to help wildlife to gain entry and exit.
If you want an ornamental pond filled with beautiful fish and nothing else then you need to decide wether you want just a Koi pond (often without any plants) or a mixture of all coldwater fish with plenty of plants. All these things need to be carefully thought about before the planning of the pond can start.
Next you will need to decide how big you want it. Then double it because no matter how much you think it will be big enough, when you have it you will undoubtedly get the ‘ponding bug’ and want bigger and better. I started with just a very small prefab and now am on pond no 4 which is much more than double the original size of my first one. The best thing to decide is how much of your garden you have to spare. If you only can have a small pond then make it deep. Anything between 2 feet – 3 feet deep is okay for most fish. Koi prefer 3ft deep. Of course you can decide to go much deeper in certain areas of the pond and also have shallows ranging from the deep to just a few inches. In our country fish can overwinter perfectly well in 2 ft of water.
Now you have decided what size you now need to decide wether to go preform, liner or mud/clay. I don’t have much experience of mud/clay ponds but I know that the water table does come into it.
Preforms are a good alternative if you don’t fancy cutting and laying a liner. They do generally come in smaller sizes and are rigid. They do need to be fitted into the ground exactly level because there is nothing worse than having water up to the rim at one end and being half empty at the other. Take your time getting this right.
The liner is my favourite choice. You can get it to fit into different shapes. It is plyable so it is easy to fit into all kinds of ledges and shelves that you want to make around the inside of the pond. Folds in the liner are a great place in the winter months for frogs to slide into keeping them safe and warm. There are different thicknesses of liner so my advice is to go for the best one that your finances can afford. The use of old carpets or felt or sand can be a good underlay for the liner to rest on and can keep any stones /old roots from piercing the liner.
The final thing to mention but actually is the first thing that you need to decide on, is what you are actually going to keep in your pond. You may be a firm Koi lover and want just Koi. I must admit that they are very pretty fish to keep but they also do need looking after. After all they are one of the most expensive of pond fish. Most people say the least your pond needs to be is about 3 ft deep. I have 2 ghost Koi and my deepest is only 2 ft deep but I am sure that if you were going to have more than a couple of Koi they do need some good depth.
Because they are going to be big fish they also need good filtration to keep them healthy. They are a fish that like to rummage in the plant roots of any plants that you put into the pond and will easily uproot them. I think this is one reason why koi keepers tend not to have plants. If this is the case with you then you also need to think about the shade of the pond. Plants can and do give shade and so you will need to find a place for the pond where it is not in full sun all day. Full sun can so often lead to green water.
Other fish that live together nicely in a pond are the varieties of goldfish such as the common goldfish, Sarasa comets, and shubunkins. Golden and blue orfe make a nice addition also. You do not really want a lot of the coldwater fish that people tend to keep in aquariums especially fancy ones. In my pond I have Ghost Koi, shubunkins, tench, comets, goldfish, golden orfe and the small native sticklebacks. These all live in a pond full of plants.
Plants are an important part of a coldwater pond. There are lots of plants to choose from and so that is up to your own personal choice but you do need a certain variety of plants. Plants that live deep, medium and marginal. Also floating plants and oxygenators.