Every migrant on board the Bibby Stockholm barge has been removed after legionella bacteria was found in the water supply.
The Home Office confirmed that the 39 men - who only took up residence on the vessel this week - are being disembarked “as a precautionary measure”.
A spokesperson said none of the migrants had symptoms of Legionnaires’ Disease, and stressed that it cannot be passed from person to person.
The development is yet another controversy to hit the barge, which is docked in Portland Port on the Dorset coast, and has been dubbed a “floating Grenfell” because of fire safety concerns.
Ministers have defended the use of the barge, claiming it is necessary to slash the £6 million a day bill of putting migrants up in hotels.
It is unclear where the migrants have been moved to or when they will be able to get back on board the barge.
A Home Office spokesperson said: “The health and welfare of individuals on the vessel is our utmost priority.
“Environmental samples from the water system on the Bibby Stockholm have shown levels of legionella bacteria which require further investigation.”
They added: “As a precautionary measure, all 39 asylum seekers who arrived on the vessel this week are being disembarked while further assessments are undertaken.
“No individuals on board have presented with symptoms of Legionnaires’, and asylum seekers are being provided with appropriate advice and support.
“The samples taken relate only to the water system on the vessel itself and therefore carry no direct risk indication for the wider community of Portland nor do they relate to fresh water entering the vessel.
“Legionnaires’ disease does not spread from person to person.”