Ponds and deep puddles are very good places for wildlife but you often cannot see it because it is all under water! However, most under water creatures (other than fish of course) need to breath and if you watch the surface of a likely pond for a while you never know what might surface.
This great diving beetle (Dytiscus marginalis) came up for a breath of fresh air right in front of me as I was looking into a pond on Wareham Common, not far from our house. We have had them in the garden pond before now and they have had to be removed very quickly as they prey on just about everything else living in it. They even attack frogs and newts!
They are certainly 'great' in that they are far bigger than any other water beetle and they cannot be mistaken for anything else. Possibly an inch long? They certainly dive, spending long periods under the surface of the water and they are beetles so I guess great diving beetle is an apt name for them.
They are not uncommon and if you find one you will often find several more, either in the same pond or close by.