Police and marina bosses have issued a warning that youths are playing with their lives with unauthorised swimming.
Officers have received 21 calls since the beginning of August about young people swimming in the marina and more about acts of anti-social behaviour.
A number of individuals have been made the subject of police dispersal orders meaning they face arrest if they are caught in the area in the next 48 hours.
Hartlepool Marina managers say they want people to enjoy the many activities on offer on the water but they should go through the right channels.
Youths face being struck by large boats and there have been complaints about young people climbing onto boats, jumping into the water and setting off fire extinguishers.
Inspector Mal Suggitt, from the local Neighbourhood Policing Team, said: “Large boats turn around in this area and people can’t easily be seen.
Youths are putting themselves in danger of serious injury or worseInspector Mal Suggitt
“Youths are putting themselves in danger of serious injury or worse and we would ask that parents remind their children of these dangers.
“We have recently identified a number of youths that had been swimming in the marina and we have visited them in their homes with their parents present to advise them of the dangers of their actions.
“We will continue to monitor the situation alongside staff at the lock office and we will put in place a dispersal notice which can enable us to disperse large groups of youths from the area.”
Marina staff yesterday wore sea safety stickers and issued advice.
Hartlepool Marina director Allan Henderson said of unauthorised swimming in the dock: “There is a very serious risk of death or serious injury.”
Rachael Forster, an on water instructor, added: “The marina is a working environment, there is an awful lot of movement in the water from large vessels.
“Nationally, there has been seven coastal deaths in the last week and we certainly don’t want the North East to be added to that.”
Hartlepool Marina runs a host of supervised activities through On Water Training including paddle boarding, raft building and powerboating.
Trigma Endurance Sports and Events also run open water swimming on Wednesday nights.
“It is about getting everybody in the water but in a safe manner,” added Rachael.