Here are a couple of pics which I took in May. The first shows the bio-filter and its overflow to a small water fall.
The second shows the overflow which we created at one section of the perimeter of the pond; this flows into a small channel which leads to a 10ft well. I have a pump in the well with which I can either pump water into the pond in the summer, or discharge in the winter after too much rain.
These pictures also show how badly green water affected the pond from March through to late May. In fact, the algae is now clearing significantly thanks to the filter and plant growth in the pond.