Not specifically answering your questions but the following link might be useful [broken link removed] and extract from Woodies DIY site:
Pondering on Ponds
One of the most relaxing sounds that sets real atmosphere in a garden is that of running water. While some people may be lucky enough to have a pond or a small stream in their garden, the majority of us are restricted to creating our own. The garden pond has become increasingly popular, as an added feature to a garden, encouraging a wide variety of wildlife from frogs to water insects and providing a well deserved source of drinking water for birds and animals.
When choosing where to position a pond, keep in mind the relaxing noise of the water and the calming view of swimming fish. Position near a patio area where you will be relaxing and spending most of your time to get the full benefit of the pond. Also make sure your pond is in direct sunlight to give light to the plants you will be growing in it. Avoid trees or overhanging shrubs as they can cause the pond to stagnate with falling leaves in autumn.
To some, the task may sound daunting, make sure you have a good team of helpers and with a few handy hints you will have a pond in no time. If you are planning on having fish in your pond, do not make the depth any shallower than 60cm (2ft). If the depth is less than 60cm (two feet) the fish will freeze in Winter. If you are not planning on having fish, you can dig to whatever depth you like. It is advisable however, that if there will be children in the garden that your pond is relatively shallow to avoid any accidents.
Choose the shape of your pond to suit the rest of your garden. The more formal garden should have a formal shaped pond i.e. square or rectangle. Features in your garden should always be consistent. Informal gardens, such as cottage gardens should have natural shaped ponds. Leave the sides of the ponds sloping so wild life will be encouraged to come into the pond. It is also a good idea to make a shelf in the pond which will allow you to sow plants at different levels creating a more natural look.
Once your pond is in place, introduce plants such as Canadian Pond Weed. Canadian Pond Weed has a specific function of giving off oxygen and uses up nutrients that would otherwise allow algae to thrive . Algae is not what you want as it turns your water green. Aim to have at least 1/2 of your area covered in pond plants, as this also reduces algae and provides essential oxygen for fish.
Give your plants about two weeks in the pond before introducing fish. It is vital that the chlorine in water is dispersed before the fish can thrive.
With a pond your garden will be open not only to a beautiful feature but also a much greater selection of plants that will thrive in moist soil. Create a bog garden beside your pond by using any excess liner. Simply dig a shallow area near the pond, place the liner in the hole and punch two or three holes in the liner to provide drainage and then back fill with soil.
Choose moisture loving plants like hostas, that have great variegated foliage and blue or white flowers - Astilbes, Bog Iris and Bull Rushes. Mimulus, in their vivid reds or oranges are ideal for a pond side and will return every year. For a larger garden, you could plant the Giant Rhurbarb (Gunnera Manicata), this big plant has huge stems with rhurbarb like leaves that can be up to 1.5 metres wide.
As I have said previously, a lot of people will create a rockery after a pond to use up the excess soil dug for the hole. Other features that go with a pond would be a trickling stream from the rockery into the pond".