The Brewery field pond is large, about 15-19m across. It is designed to be able to withstand drought which is expected in this part of the country, especially recently.
So even when the central area of water recedes, the areas left behind are all over-layed with a geotextile that protect the pond liner from the sun, from dogs claws and other traffic and also means you don’t have to look at black plastic! The pond is topped up by the rain collected from the shelter.
Here is a visual of the pond brimming. It won’t always be like this, but what we need to remember is, the highest biodiversity to be found in a pond is in the muddy drawdown zone which naturally fluctuates throughout the year. A pond with periodically low muddy sides is a good, not a bad thing for biodiversity.