Contractors started work on the Green Lane facilities early in the new year on what was expected to be a 20-week project.
However, the contractors have gone into administration and Northumberland County Council is now seeking a replacement.
A council spokesperson said: "Unfortunately, the refurbishment works have been delayed due to a combination of factors - most notably the contractor going into administration.
"There has also been changes to the specification to further improve the overall quality and standard of the facility and help with future cleansing/maintenance arrangements due to Covid.
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"We appreciate that the current temporary toilet provision is having to cope with very high visitor numbers to the island at the moment and we are cleaning and servicing these regularly to help meet the demand. There are also two accessible portable toilets suitable for those with disabilities.
"We are continuing to source a new contractor to finish the work and our priority remains the completion of a high-quality public toilet facility including new Changing Places accessible toilet provision, as soon as we possibly can."
The refurbishment scheme will include replacement of the mechanical and electrical installations, replacement of all sanitaryware, refurbishment of the internal fabric to the buildings, and creation of a new ‘Changing Places’ fully accessible disabled toilet facility.
The council has already approved a £1million capital investment in public toilets.