On 2 July 1816 Méduse ran into increasingly shallow water, both Chaumareys and Richefort ignoring signs such as white breakers and mud in the water. Eventually, Lieutenant Maudet took it upon himself to start taking soundings off the bow, and, measuring only 18 fathoms, warned his captain. Realising the danger at last, Chaumareys ordered the ship brought up into the wind, but it was too late, and Méduse ran aground 50 kilometres off the coast. The accident occurred at a spring high tide, which made it difficult to re-float the frigate. The Captain refused to jettison the 14 three-tonne cannons and so the ship settled into the bank.
Plans were proposed to use the ship's launches to ferry the passengers and crew to the shore, 60 miles away, which would have taken two boat trips. Numerous ideas for lightening Méduse and immediately coming off the reef were proposed, in particular, that of building a raft to unload Méduse's cargo. A raft was soon built; it was 20 metres in length and 7 metres in width, and was nicknamed "la Machine" by the crew. On 5 July, a gale developed and the Méduse showed signs of breaking up. Passengers and crew panicked and so the captain decided to evacuate the frigate immediately, with 146 men and one woman boarding the woefully unstable raft, towed by the boats of Méduse. The raft had few supplies and no means of steering or navigation. Much of its deck was under water. Seventeen men decided to stay on the Méduse, and the rest boarded the ship's longboats. The crew of the boats soon realised that towing the raft was impractical and began to fear being overwhelmed by the desperate survivors on the raft. It was decided to cut the ropes, leaving the raft and its occupants to their fate. The lifeboats, including the captain and Governor Schmaltz aboard, then sailed away to safety. Some landed immediately on the coast of Africa, most of the survivors making their way overland to Senegal though some died on the way.
On the raft, the situation deteriorated rapidly. Among the provisions were casks of wine instead of water. Fights broke out between the officers and passengers on one hand, and the sailors and soldiers on the other. On the first night adrift, 20 men were killed or committed suicide. Stormy weather threatened, and only the centre of the raft was secure. Dozens died either in fighting to get to the centre, or because they were washed overboard by the waves. Rations dwindled rapidly; by the fourth day there were only 67 left alive on the raft, and some resorted to cannibalism. On the eighth day, the fittest began throwing the weak and wounded overboard until only fifteen men remained, all of whom survived until their rescue on 17 July by Argus, which had accidentally encountered them.