Here are some important points to consider when planning your pond or lake.
Why not build your pond away from overhanging trees? The leaves they drop will decompose and produce nitrates that encourage algae growth. Build your pond or lake in a location that is exposed to sunlight for about half the day.
Even a small pond should be at least 60cm deep at one point to prevent oxygen levels from dropping too low when the surface freezes (to protect invertebrates/amphibians). If you intend to keep fish in your pond, the deeper areas are vital to protect the fish from herons and cats.
Have at least one shallow side, some of which must be well planted, for the amphibians to get out of the water. The shallow sides allow for more fringe plants, which in turn support more wildlife. The slightly sloped sides allow hedgehogs to escape and are less of a hazard if a small child falls. Toddlers or young children should always be supervised near water.
Before digging your pond or lake, make sure there are no sewer, water or electricity cables in your yard, check with your local utility companies or local council. Planning permission may be required, depending on the size of the lake or pond and the area.
Be aware that any tree roots near your pond or lake bed can break through your liners and cause future leaks.
Before introducing fish, be aware that fish eat invertebrates and tadpoles, and avoid damselflies and dragonflies; Generally speaking, the widest variety of natural life can be found in ponds that do not contain fish.
Do not locate your pond on marshy ground, otherwise the water will tend to rise up behind the liner and cause problems in the future. If you have no choice but to dig a small pond in an area with a high water table, one or more sumps can be dug around the pond with pumps inside to artificially lower the water table (although this is a complicated and expensive solution).
After the lake has been excavated, it is common practice to use a layer of soft sand to smooth the surface. For the underlayment, a geotextile membrane is best (you could cut costs with a polypropylene mat, but remove the nails/tacks first). There are many different liners now available, Butyl is a popular choice because it is strong and durable, but polyethylene is sometimes used. The lining is usually covered with softer sand and fine gravel washed before the pond or lake is filled. Some pond and lake beds are constructed of concrete, often incorporating liners. The traditional method is to use puddled clay, however this is difficult and expensive and is therefore rarely seen in new ponds and lakes. Lake construction techniques are constantly changing as technology advances, be sure to seek the advice of several different contractors to decide on the best system for your project.
Please note this article is for advice only, always consult a trained landscaper before attempting any groundwork.