Boaters on the Thames have been warned about a gang of yobs after a spate of summer mayhem at Oxford's Iffley Lock.

A 61-year-old man was pushed into the river, a canoeist stoned, another tipped out, a digger driven into a fence, and logs thrown into the water over the past few days at the normally idyllic beauty spot.

More police patrols are being mounted and extra lock keepers have been drafted in.

Environment Agency spokesman Tim Abbott said: "It is not really the damage to the area that is most distressing, but the antisocial behaviour.

"We have doubled the number of staff we have down there, so the lock keepers are never left there on their own. We have been warning boats at other locks."

Thames Valley Police spokesman Tim Wiseman said a man was pushed into the river as he walked along the lock at 6.50pm on Sunday after five boys told him to look at fish in the water.

He said: "He was helped out by another man who was passing by. He was taken to the John Radcliffe Hospital and was quite shocked."

He said on Saturday, up to 20 youths threw stones at a canoeist, while on Monday, at 6.30pm more youths were seen throwing stones.

A 17-year-old arrested on suspicion of assaulting the man pushed into the river has been released on police bail.

Mr Abbott said problems began last Wednesday, when staff saw a cyclist surrounded by the youths and spotted one yob defecating on a footbridge.

He said on Thursday timber was thrown in the river and a man was tipped out of his canoe, while on Friday youths were seen throwing stones at people.

Mr Abbott added: "On Saturday, a JCB digger was driven into a fence."

A woman who witnessed the digger incident, but did not want to be named for fear of retribution, said: "There were about five or six of them around the digger and one on it, who reversed it into some fencing."

Call police on 08458 505505 with information.