Update: according to the Echo the search "for a 25-year old man" is continuing Sunday.
A search and rescue operation was mounted at around 10pm on Saturday night (Feb 13) which will have been heard by many in Bitterne Park and St Denys, and which appeared to centre around areas near Cobden Bridge.
The search involved a helicopter with search lights, and teams on foot searching the riverbanks with torches. It was reported a boat was also used later on in the search.
Hillhead Coastguard Rescue Team tweeted it had been a search, with coastguard and police, for a missing person.
The Daily Echo quoted police, saying it was a"concern for welfare", but said further details weren't given.
Operations appeared to be called off around midnight.
We hope everyone's safe.
Cobden Bridge on Saturdayt evening (Feb 13)
Sam Ridout tweeted this route map apparently taken by the helicopter.
That explains it! Hope everyone is safe and ok. @bitternepark pic.twitter.com/QcrwNeCADH
— Sam Ridout (@sridout92) February 13, 2016