A live juvenile humpback whale is stranded at Sandy Bay, the City of Cape Town said on Sunday.
In a statement it said law enforcement officers had since closed the beach.
The public has been urged to stay away from the area.
Environmental affairs officials were at the scene.
A decision had been made to euthanise the whale.
"Once the process has been concluded the carcass will be towed to the Hout Bay harbour from where it will be taken to the landfill site at Vissershok," the city said.
"The public is requested to avoid Sandy Bay beach and the Hout Bay harbour during the course of the day as the operation will only be completed late this evening."