- John Wood, Scott Hart, Roger Barton
- 166.62 square metre(s)
- Australia (Sydney)
The largest flag unfurled underwater measures 166.62 m² (1,793 ft² 70 in²), and was achieved by Roger Barton (UK), John Wood and Scott Hart (both Australia) in Sydney, New South Wales, Australia, on 5 December 2017.
All divers involved in the attempt used scuba diving equipment. The flag chosen to be unfurled was the Argentinian flag.