Geograph - photograph every grid square

Shown on Ordnance Survey as a 'Balancing Pond'; one of several.

Also known as attenuation ponds.
"They have to build them in developments over a certain size. The idea is to maintain the waterholding capacity of the land prior to development. It doesn't necessarily mean the area is prone to flooding. How often it holds water will be dependent on the weather and the soil type

They are left untamed, and aren't attractive in a typical manicured garden sense. But they often hold more nature in a real sense than a number of overly mono-cultured gardens combined."
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