Surfers have said they fear "a nasty accident" after jet skis were seen passing within a few feet of people in the sea.
One jet ski was filmed cutting in front of a group in Bournemouth, while another emerged from under the pier.
Bylaws governing the use of watercraft at Bournemouth beach only apply between the months of April and October.
Bournemouth Borough Council said it had "little power to enforce restrictions outside of the bathing season".
Part of the incident was filmed by Tom Saunders on Sunday lunchtime near Bournemouth Pier.
Surfer Andy Myers said: "It is only a matter of time before there is a nasty accident, or worse."
'Too fast, too close'
Mr Myers, who was in the water, said a small group of jet skiers had been visiting the area in recent weeks and jumping the waves close to people in the water.
He said: "There seems to be a small group of people who are acting recklessly. One guy landed right next to me.
"I don't think trying to regulate everything is the way to go. It's almost impossible to enforce and it doesn't seem fair on the people who are behaving.
"I think it's about making awareness and dialogue. We've got other jet skiers out there who are totally fine."
Local bylaws state that personal watercraft must not "endanger other beach users" if they are within 200m of the low water mark, but the regulations only apply between April and October.
The Maritime & Coastguard Agency said: "The majority of jet ski users are responsible, but in the past we have received complaints that set skis have gone too fast and too close to shore. This is a concern to us as it's putting swimmers and other beachgoers in danger."