Lives are being put in danger by anti-social youths at a riverside, boat owners say.
A scorching summer brought crowds to a lock in Yalding, near Maidstone, sparking fear and concern from boat owners.
Boat owners share their concerns with KMTV
One owner said bottles were thrown at him and his partner while they were travelling through Hampstead Lock.
He said: "We were trying to pass through the lock when a one litre vodka bottle nearly hit my partner.
"It could have killed her. If the bottle had hit her head she would've been knocked unconscious and could have fallen in the river.
"There were at least 60 teenagers all drinking underage, we felt quite exposed going past them."
Moments later a beer bottle struck the 50-year-old boat, showering them with glass.
Mark Smurthwaite, chair of Medway River Users Association, said: "It's only a matter of time before someone gets seriously hurt, then the wrong people will get the blame.
"These children are jumping on boats, swimming in the water completely unaware there's one or even two propellers in the water.
"They've got no respect for other people or their property. It's probably over for this year but we need to be prepared for next summer."
The owner of one nearby marina, says the Environment Agency-owned lock is fast becoming a "no go" area.
They said: "Each year the problem gets worse.
"River users used to have picnics at the lock, now people stay well clear, which is a huge shame.
"If the Environment Agency would put some signs up saying it's private land, or some fencing, that would help.
"If there were a disturbance at least a police officer could point to a notice and say you're on private land, but when there are up to 70 of these youths it is quite intimidating."
Insp Mark Hedges, of the Maidstone Community Safety Unit, said: "Kent Police is aware of the concerns of some boat owners at Hampstead Lock, Yalding regarding anti-social behaviour in the area, particularly during the summer months when sometimes young people want to swim in the river.
"We are continuing to work pro-actively with our partner agencies to reassure boat owners that we take all forms of antisocial behaviour seriously.
"Our PSCO for the area has spoken directly with a number of young people in the area to explain the effects of anti-social behaviour on others.
"Medway river users should continue to work with us, report incidents, keep a diary of events so we can continue to target the small minority whose actions can cause distress and anxiety to others."