- Oceanum Liberandum
- 842 people
- Portugal (Sesimbra)
The most participants in an underwater clean-up in 24 hours (single venue) is 842 and was achieved by Oceanum Liberandum (Portugal) in Sesimbra, Portugal, on 28 May 2023.
The attempt had to be paused for about 2 hours due to an unexploded world war ii bomb being discovered underwater, however the 24hr clock continued to run. The bomb was detonated under a controlled explosion out at sea