A Great White!
Not a shark but an egret.
I met a woman who had just left a hide at Amwell. She wanted to talk kit and birds, though she didn't know much about either. She had photographed a big white bird, which I guessed was the great egret that has been seen here recently. She showed me the image on the back of her camera and said the bird had flown off.
As I approached the hide the big bird flew over and I got my first ever sighting and image. Once in the hide I got a series of shots of a pair of coots mating. Then the great egret flew into view. It was being harried by the black-headed gulls. These birds were quite rare and first seen in the UK in around 1989. A pair bred in the UK for the first time in 2012. By 2021 they were no longer classed as rare. They are about the size of a grey heron with longer legs and neck. They differ from the little egret in that they have dark feet and a yellow bill.