A watersports centre has urged people not to swim in its lake without permission, warning they might not be rescued if they get into difficulty.
Welton Waters Adventure Centre, near Brough, said it had seen groups of young people entering the water after accessing the site via a footpath close to the Humber Estuary.
Esther Towns, an administrator at the site, said the area where the group was seen had thick weeds which could hamper safety boats reaching them in an emergency.
She said: “Those children could come here and pay for a buoyancy aid or a wetsuit for a very small amount and they could just be doing it safely.”
In May, the centre issued a warning over the dangers of mixing open water swimming with alcohol.
In a social media post on Tuesday, officials from the activity centre said they were concerned about people taking unnecessary risks.
“We have been cutting the weeds but there is still a large area we have yet to cut, and the prevailing winds have pushed the cut weeds into that area too,” the post stated.
They encouraged people to “talk to the young people in your family and help them stay safe”.
“There were a number of tragic and often preventable deaths in the half term break, and we do not wish to see these numbers added to,” it added.