The vessel is idled in the French port of Marseille until further notice while its operators – the NGOs SOS Méditerranée and Doctors Without Borders (MSF) – desperately try and clarify its flag notice so that it can resume rescue operations.
The Aquarius had first been flying the flag of Gibraltar and then that of Panama but in September the Central American country's maritime agency said it would remove the vessel from its registry – a moved SOS Méditerranée said was the result of political pressure from Italy.
But hopes that Switzerland could provide a lasting solution to the ships' flag problem have been dashed after the Swiss Federal Council, the country's executive, on Monday rejected a proposal that would have seen the Aquarius registered in Switzerland.
⚡️The Swiss Federal Council halts SOS MEDITERRANEE'S return at sea:— SOS MEDITERRANEE (@SOSMedIntl) December 3, 2018
The humanitarian organisation regrets the incoherence of this decision. https://t.co/OamnykWUFe
Responding to the proposal put forward by Greens MP Aline Trede with support of colleagues from the Socialists, the Christian Democrats and the Liberals, the Federal Council said it saw no legal obstacle to registering the ship in Switzerland.
But the Swiss executive said migrant rescues in the Mediterranean needed a coordinated and long-term approach. Ad-hoc negotiations for every ship that sailed around with migrants on board did not make sense, the Federal Council argued.
Instead, what was needed was a coordinated European effort based on marine rescue rules, safe disembarkation points and a mechanism for the sharing out of refugees.
The government said this was not currently the case and that individual actions carried out by ships like the Aquarius threatened to undermine international cooperation.
For this reason the ship would not be registered in Switzerland.
The Aquarius was at the heart of a diplomatic dispute between Italy and its neighbours earlier this year, when both Italy and Malta refused to allow it to dock with more than 600 rescued people aboard. The ship remained stranded at sea for over a day until Spain eventually offered it safe harbour.
In November, prosecutors in Sicily ordered the seizure of the Aquarius to investigate allegations that MSF illegally dumped potentially hazardous waste at Italian ports.
The order means that if the Aquarius were to return to Italian waters it could be seized.
MSF have strenuously denied the prosecutors' allegations which it called the "umpteenth trumped-up attack [on the part of Italian authorities] to block MSF's life-saving activities at sea".