If you want a healthy pond, sunlight is essential, but you need to consider the complex balance of the plants and fish that live within your pond, too much sunlight can give you problems, too little will also have its problems, so a balance of sun and shade is where you need to be.
Choosing where to site your pond is one of the most important decisions you need to make, get it right and you will have a healthy pond, get it wrong and you could be fighting a loosing battle.
Sunlight is the main source that keep oxygenating plants doing what they do best which is produce oxygen.
The oxygen generated from these plants stops your pond water from stagnating and getting smelly, what they do is create a healthy environment for fish and plants that live in the pond.
That said too much sunlight can raise the temperature of your pond, increasing the growth of algae and lowering the amount of oxygen available to your fish.
Algae will thrive in sunlight and will use up the oxygen in your pond leaving less oxygen for your fish.
The size of your pond also has an effect, a large deep pond will not suffer as much as a small shallow pond.
A deep pond offers your fish an area to go if the surface temperature gets too much, a shallow pond will not offer any safe place for your fish to go, also a shallow pond will heat up more than a deep pond.
If you can find a spot in your garden that offers both sunlight and shade throughout the day that’s the place to have a pond.
If you can only find an area that’s in full sun throughout the day you can add your own shade, this can be done with plants and man made structures such as a canopy that can cast shade over your pond.
Aquatic plants such as water lilies and water hyacinth can also be used to shade the water from the sunlight.
Too much shade is bad for your pond if you have fish but will be ok if you want a wildlife pond.
What you’re looking for is a balance of about 4-6 hours of sunlight a day and the rest in shade.