This is one of the biggest myths surrounding water gardening today. Most books say a pond needs a minimum of 4-6 hours of sunlight a day for aquatic plants to live. They discourage building a pond in a shady area.
The truth is that aquatic plants do bloom more and flourish better in high sunlight conditions. This is not debatable. What is debatable is how well aquatic plants can do in low light conditions.
With less sunlight, plants will need more fertilization. Time release aquatic plant fertilizers do an excellent job of promoting bloom and foliage growth. Also make sure plants have enough room to grow. Plants left in containers become root-bound and their growth is stunted.
We have even installed ponds inside where there is no sunlight at all. If you have aquatic plants that are shade lovers, they do great and the pond looks wonderful too. So instead of limiting your options by following defined rules, such as a pond’s sunlight requirements, adapt your installation procedures accordingly.
Full-shade ponds will have fewer blooms then full-sun ponds but they will also have less string algae. Algae likes sun too!