Alliance Party MLA Kate Nicholl said children’s safety is of “paramount importance” and urged young people to be “sensible” and parents to be vigilant.
“What can seem like a fun situation can turn dangerous so quickly,” added the Belfast South assembly member.
Nicholl said that at the time of night the children were entering the water, no immediate help is available if something goes wrong.
She is encouraging parents to speak to their children about water safety and the risks of swimming at night.
“It actually doesn’t matter what age you are,” she said.
“No one should be trespassing full stop but no one should be swimming there at that time of night.”
Sinn Féin councillor Daniel Basset added: “I will continue to engage with local bodies, the owner and the local community to help stop these incidents from happening within our area.”
Social Democratic and Labour Party councillor John Gallen also appealed to young people and families about the dangers of going into the lake at night and it is extremely dangerous and “we don’t want anyone to drown”.