The asylum seekers who arrived on the Bibby Stockholm barge this week are being removed after Legionella bacteria was found in the water.
The Home Office has said 39 people have been removed after samples from the water system showed levels of the disease-causing bacteria.
Migrants began arriving on the Bibby Stockholm barge docked in Portland off the coast of Dorset on Thursday.
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.
“Following these results, the Home Office has been working closely with UKHSA and following its advice in line with long-established public health processes, and ensuring all protocol from Dorset Council’s Environmental Health team and Dorset NHS is adhered to.
“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.”