BOATERS on the Thames have been warned about a gang running amok on the river after a number of incidents 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.

Now the Environment Agency is warning boaters who travel through Osney and Sandford locks to be wary, while extra lock-keepers have been drafted in to boost security and police are increasing patrols.

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

"It is the psychological side of it for our staff, who feel under siege.

"We have doubled the number of staff we have down there, so lock-keepers are never left there on their own.

"We have been warning boats at other locks, letting them know what is going on ahead.

"We have done it quite informally. We don't want to panic the boaters."

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 then pushed in, sustaining a grazed ankle and hand.

"He was helped out by another man who was passing by. He wouldn't have been able to get out on his own.

"He was taken to the John Radcliffe Hospital and was quite shocked."

He said that last Saturday 15 to 20 youths threw stones at a canoeist, while on Monday at 6.30pm more youths were seen throwing stones.

Mr Abbott said problems began on Wednesday, June 7, when staff saw a cyclist surrounded by the youths and spotted one yob defecating on a footbridge.

The next day timber was thrown in the river and a man was tipped out of his canoe, while last Friday youths were seen throwing stones at people.

Mr Abbott added: "Last 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 reprisals, said: "There were about five or six of them around the digger and one on it, who reversed it into some fencing.

"They had taken it out and caused a lot of damage."

Billy Carr, landlord of the Isis Tavern, not far from Iffley Lock, said: "The yobs hot-wired the JCB and were joyriding around in it at the back of the pub.

"I also saw them on Wednesday unmooring a boat which was tied up outside."

Brian Richards, 53, of Cowley, who regularly walks along the river, said gangs of youths in the area were intimidating elderly people.

A youth aged 17 has been arrested on suspicion of assaulting the man pushed into the river.

He has been released on police bail.