Lincolnshire Police are carrying out underwater searches in River Witham at Waterside North after a man was charged with assault in Lincoln.
The Tactical Support team and the Underwater Search Unit are at the location off Broadgate in Lincoln since after midday on Tuesday, March 10.
Divers are in the river performing searches. The reporter on the scene saw them retrieving a knife from the water.
The investigation follows an assault on St Rumbold Street on March 7.
Layton Hudson, 25, from Clarendon Gardens, Lincoln was charged with an offence of GBH and appeared at Lincoln Magistrates Court on Monday, March 9.
He was remanded in custody by the courts and the case has been sent to Lincoln Crown Court.