Big fish (trapped) in a very small pond.

This fish lives in a pond on Whitehall Meadows, a local nature reserve, less than a mile from my house. It is notorious, enigmatic and trapped. Few people believe it exists. Those who know it does have been having a real struggle persuading the rest that it is real. This photo is clearer than any photo of Nessie. It proves the existence of the fish.

Can anyone help me to identify it?

It seems to be perhaps 40 or 50 cm in length, possibly longer - I've never glimpsed the whole thing because of all the weed.

The pond is about three meters by three meters and probably less than half a meter deep. It is covered in weed as you can see. It also contains various items of detritus from the "civilisation" we are part of (beer cans, a coke bottle, a nondescript blue plastic bowl, a plastic bag). As the hot weather has gone on the pond has shrunk (although tonight's rainstorm will have helped reverse that trend). If the lovely summer weather continues this poor fish is bound to die.

In other news; I went back to work today (a half day, but quite busy) and my lovely daughter Emily is off to France tomorrow.