The Croydon underpass was closed earlier today after a teenager was seen to throw an item over the wall.
Plain clothed officers on patrol came across a group of youths close to Fairfield Halls at about 1.10pm.
One of the youths made off and threw an item into the underpass.
A police spokesman confirmed officers briefly closed the underpass on Wellesley Road and recovered a knife.
A male believed to be in his late teens was arrested on suspicion of possession of an offensive weapon and remains in police custody.
The road has since reopened.
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules hereComments are closed on this article