Location, Location, Location
Ideally, your pond needs be positioned in partial shade.  Ponds that are in full sunlight generally attract more algae growth and this leads to an unpleasant green hue to the water. 

You need to pick a location which is away from deciduous trees (trees that shed their leave), because autumn leaves will settle on the water surface and sink, creating unwanted and undesirable debris on the pond floor.  
 

The Depth Of Your Imagination
If the proposed pond is purely for decoration (i.e. no fish), you should consider a minimum water depth of 0.6 metres,
to allow the environment to reach a dynamic equilibrium with its surrounding environment and not need constant attention.

Decorative fish need a depth of around 0.6m - 1m.  

Whilst Koi Carp or larger fish require a depth of 1m -1.5m.

During the winter, the deeper water will remain a few degrees warmer than the surface, offering greater freezing protection and a more comfortable area for the fish to semi-hibernate.

A Water Tight Barrier
There are a number of materials you can use to create a water-tight barrier in the excavated hole.  
Plastic and Fibreglass liners can offer instant contouring and are highly durable if installed correctly.

Flexible rubber liners, do however offer more control over the pond size and shape, and are also very economical to install and can last a lifetime if they too are installed correctly.  If you are going to use a liner, we’d recommend using a Protective Underlay beneath the liner, to safeguard against root penetration and potential puncturing from stones, rock or flint.  

Get In Shape
If you are planning to use a flexible rubber liner, there are no real restriction on the the shape or size of the pond, unless it is extremely large, then you may need to see planning permission, and/or local environmental health permission.

Informal ponds tend to be more curved, more natural forms whereas formal ponds generally have sharper lines and are often square or rectangular in shape.  

Being On The Level
Ideally, the proposed area should be level, but this is not always practical, so you’ll have to develop some landscaping skills using a line and spirit level to estimate how far down you’ll need to dig to achieve a consistent water level line, that looks natural and is in keeping with the contours of your ponds surroundings.

Marking Out & Digging
You’ll need to mark out the basic pond shape on the ground using some sand, string or a spray marker (from most DIY stores).
Once you are happy with the final outer shape, you can begin digging the perimeter with a spade, remembering to dig inwards from the outside edge.

The inner section of the soil can then be removed and located to another area away from the site to prevent the possibility of an avalanche or collapse as it begins to mount up.

If you plan to add a marginal shelf for planting, dig the surface soil to a depth of around 30cm.

Digging The Deep Water Zone
The inner deep water zone can now be marked out and the soil excavated to the full pond depth.  
Ensure the sides of the pond are sloping inwards to prevent the soil collapsing.  

Allow a 30-50cm perimeter 'shelf' for the marginal zone, which should be sufficient for planting baskets to be mounted on once the liner is fitted.

If you would like to create a stream or waterfall, some of the excavated soil can be used to create a raised bank which can then be covered using a flexible liner. Be sure to contour the bank well, so it blends into the environmental surroundings.
Nothing looks worse than a pond with a hump at one end, the trick is to make it look natural.

The Top Trench (Capillary Barrier)
It's a good idea to create a small perimeter trench around the top area of the pond, this will prevent water from saturating the surrounding soil.  
The Underlay and Flexible Liner can then be folded over this lip and around the trench behind.  
The gap can then be back-filled with pebbles or a suitable material, creating a physical barrier between the relatively dry soil edge and the start of the pond's 'wet' side. 

Measuring & Selecting Pond Liners
Using a long length of string or a long tape measure, start at one end of the pond (around 0.5m from the pond edge to allow for pleating and folding where required) and follow the contours of the pond with the string or tape.  
Finish at the far side of the pond (again, around 0.5m onto the ground from the pond edge).  The measure the total length of the string - this will determine the total length of the required liner.  Repeat the process to determine the total width of the liner.

It is generally recommended to get the best quality Pond Liner you can afford because cheaper liners do not offer the same excellent stretch characteristics that make it easier to pleat and fold them.  

If in doubt, we can help you with your pond liner size calculations.

Fitting A Protective Underlay
Protective Underlays are usually supplied in a 2 metre wide roll and is very easy to fit.  Simply roll out the underlay and form around the pond contours.  Allow at least 15-20cm overlap between sheets to ensure that a long lasting barrier against roots and stones is achieved.  Any excess underlay around the pond perimeter can be cut with a sharp knife or scissors.  

If the soil is particularly flinty, alway try to remove as many stones as possible before installing the liner.  It is also a good idea to place a layer of sand on the base of the pond, but this is generally unnecessary when using a good quality pond underlay.

Fitting A Flexible Pond Liner
Unroll the pond liner, being careful not to damage or tread on the liner itself.  If the liner is large, it's worth borrowing a few friends or family members to help lift it carefully into place.  

Once the liner is positioned over the top of the pond, flap the liner to allow air underneath and allow it to sink into the deepest section of the pond.  

Step inside the pond (taking shoes off is a good idea at this point to avoid puncturing the liner) and gradually push the liner into the pond contours.  Pleat and fold the liner as neatly as possible, the better you do this, the neater and more natural your finished pond will look.

DO NOT CUT OFF ANY EXCESS UNTIL THE POND IS FILLED WITH WATER, as the weight of the water is likely to pull a little extra liner inwards, so cutting prematurely could make your liner too short in places.

Fitting A Liner On A Watercourse Or Waterfall
A gentle stream or waterfall is a lovely way of bringing the soothing sound of moving water to the pond.  
If you have chosen to create a banked area, this can be lined with protective underlay and another sheet of flexible rubber liner over the top.  This liner can be joined to the main pond liner using a flexible underwater sealant.

Carefully ensure that there are no creases on the adjoining liner surfaces.  Degrease both the watercourse and main pond liner and apply the adhesive in multiple rows to ensure a permanent bond.  Press the two liners together gently and allow the sealant to cure before filling the pond completely. It’s best to leave it overnight (when there is no risk of frost) for best results.

Choosing Pond Pumps & Water Filters
It is really important to maintain a healthy environment for fish and other pond life, so a pump and filter system is definately recommended.  The submersed pump will supply water to a filter box, which is usually mounted on dry land near the pond edge.
Or you can buy integrated filters and pumps.

 The filter will clean the water and this is then returned back to the pond on a continuous basis.  
Many separate Filter Systems include an Ultraviolet Clarifier and Centrifugal cleaning systems, with the former being able to kill suspended algae ('green water') and clump this together.  The algae lumps are then removed from the pond and broken down by the 'friendly' aerobic bacteria which live inside the filter box.

Planting Out Your Pond
Adding plants to a pond will not only increase its aesthetic appeal but will also help to reduce excess nutrients in the water.
Water Lilies are an excellent choice as they also offer shade for pond dwellers.  Water Lilies are suited to deeper water areas, generally in depths of 0.6 - 1.5 metres and can be planted in baskets to help keep the pond base free of soil and debris.  

Shallower water areas such as marginal shelves can be planted with flowering marginal plants, and using pond baskets is a great way to do this.

Pond & Garden Lighting
Adding strategically placed lights in the pond can create a whole new dimension, allowing you to enjoy the feature into the evening.  

Pond Lights can be fully submersed and are ideal for illuminating streams, water features and fountains.  
Pond Lighting can also be used to highlight planting areas and can look beautiful in winter and warm summer nights.  

Pond Fountains
A pond fountain display can be used to add drama and water sound if desired.  Fountains also help to aerate and circulate the pond water.  

A fountain usually consists of a submersed pump, a rigid tube ('riser') and a fountain nozzle.  Different nozzles can be used to create a completely different water display.  

Adding Water Features
Water features usually consist of a static object such as a stone column, tubes or sculpture which water is then pumped to.  
The water then cascades down the feature. The use of underwater lighting can also further enhance their visual appeal.