Marine conservationists have urged Scarborough Council to scrap plans to install boulders in front of the Spa after a teenager got stuck in rock armour near Whitby.
The Sons of Neptune has written to the authority to highlight the incident and have urged leaders to extend the public consultation period.
It is the latest attempt by the group to highlight £16 million plans to overhaul battered Victorian sea defences, which will see rock armour installed on the beach below the Grade II listed theatre.
Firefighters, including a crew from Scarborough, were called to the eastern side of Staithes last Monday night following reports that a 15-year-old had slipped and trapped his leg when fishing for mackerel.
They managed to free him by forcing the rocks apart and he escaped unharmed.
However, it has sparked an urgent warning from the Coastguard to stay away from rock armour amid fears the boy could have died if the tide had come in.
Freddie Drabble, leader of the Sons, said: “The youth could have lost his life. The council are therefore on notice of the danger they will be creating. Perhaps it is time to ask which councillors are holding their hands up now to admit personal responsibility when the inevitable happens.
“Indeed there would have to be warning signs and a degree of fencing off which still would not avoid the council’s legal liability towards any child injured or killed.”
An online petition objecting to the proposals has so far attracted 2,000 signatures in just three months.
Mr Drabble added: “How much greater is that risk of a fatality or serious accident increased when the area proposed for rock armour directly adjoins a children’s play area? Indeed the entire area of Children’s Corner would effectively be turned into a rock climbing challenge.
“The Sons are asking that all these concerns will be taken into account when the rock armour proposal is next considered by the council.”