Outdoor swimmer Simon Griffiths has sparked a debate after he captured images of thousands of small fish in the Thames.

Simon was mystified about exactly what they are and just why so many gathered in the same spot close to Teddington Lock.

He posted a video clip and images on Twitter and challenged people to identify them.

© Simon Griffiths / Outdoor Swimmer

He wrote: "I've just seen thousands of small fish in the Thames, just below the weir at Teddington Lock, facing upstream but barely moving. Does anyone have any idea what they are and what they are doing?"

Simon, a veteran of swimming in the Thames, told Nub News: "I don't know what they are.

"One person on Twitter said mullet fry (but then had second thoughts) and a second thought break fry, which seems the most likely."

Asked about the health of the river, he said: "The clarity is amazing at the moment. I've never seen it like this but I think that's a reflection of the small amount of rain we've had this summer.

"As swimmers we usually only worry about the water quality after heavy rain that can result in sewage discharges and storm drain spills."

Fishing guru and Richmond's own 'man of the river', Keith Arthur, a presenter of Tight Lines on Sky Sports for many years, has his own theories.

He said: "They could be genuine freshwater fish, probably dace (I think they are too wide for bleak as suggested); they could also be mullet which, although a saltwater fish are very happy in freshwater.

"As we've had so little rain, very little freshwater is coming down the river and, with big tides last week, saltwater fish such as mullet and bass, which breed in the estuary with fry venturing as far upstream as Teddington, would naturally appear further upstream.

"There's also a chance they could be smelt, which come up the river in large shoals in late summer to spawn in freshwater."

If they are smelt, they can be eaten whole - fins, backbones and all! They're simply gutted, rinsed, tossed in batter and fried.