The pair, aged 15 and 16, had been walking near a tidal creek before they became stuck in mud up to their waists at Wat Tyler Park, Pitsea, Essex.
One used his mobile to ring his mother, who alerted emergency services at about 15:30 BST on Saturday.
The boys were hauled to safety by rescue teams after a police helicopter was used to locate them.
Paul Chipperfield, of Essex Fire and Rescue, said crews arrived to find the pair stranded about 20ft from land and "suffering from shock and the cold".
Essex Police said they were checked over by paramedics and found to be unharmed.
Two teenage boys have been rescued from a muddy marsh after one phoned his mum for help.