Firefighters and Coast Guard crews worked to rescue him using specialized mud rescue equipment.
The child, who lived on site, was washed away with a fire hose before being wrapped in a blanket. He was unharmed.
Walking on mud ‘can be very dangerous’
Barry Darbon, a Portishead Coast Guard officer, said: “The boy was walking his dog when he got stuck in the mud.
“He was only about 10 meters in the mud when he got stuck.
“This incident just proves that even if mud looks solid, you never know if there is an air pocket in the mud that could burst and trap you.
“People need to understand that walking in mud can be very dangerous.”