The individual, along with two other subcontracted staff who were working on CMAL's £1million project to upgrade the harbour, are now self-isolating in holiday accommodation on the island.
CMAL says it has strict Covid-19 guidelines in place to protect employees, contractors and communities living near its harbours projects and stressed it has made it clear to all contractors they must follow those rules stringently at all times.
This is the first case of infection CMAL has experienced across all its projects in the past 12 months.
The site was shutdown but work resumed on Tuesday March 23.
A CMAL spokesperson said: 'On Friday March 19, an employee of a subcontractor tested positive for Covid-19. As part of our Covid-19 guidelines, all site workers were tested before travelling to Colonsay and all tested negative. In addition, following the positive case, all workers have been tested on Friday and Monday. There have been no further positive cases.
'We have strict Covid-19 guidelines in place to protect our employees, contractors and the communities who live near our harbours projects. We have made it clear to all our contractors that they must follow the guidelines stringently at all times.
'For the past 12 months throughout the pandemic, our harbours and engineering teams, with the support of contractors, have continued to provide maintenance and repairs for essential lifeline ferry services. In a year, this is the first case of infection across our team and all our work and projects.'
In October last year CMAL, working in partnership with NG Marine, gave public reassurance it had implemented special measures to help prevent the spread of Covid-19.
The contractor and site works would be self-contained and working patterns were arranged to minimise the number of trips on and off the island. In addition, construction materials would be delivered in bulk to minimise journeys, a statement said.
The project is part of CMAL’s routine harbour maintenance programme to help to prolong the life of the concrete pier and improve the facility for current vessels.
Lee Rankin, civil engineering project manager at CMAL at that time, said: 'We understand the local community may feel apprehensive about construction taking place now in the context of the coronavirus pandemic, but we are adhering to strict health and safety guidance and using a range of measures to protect our employees, contractors and the island community.
'We don’t want to delay the project because it’s needed to strengthen the existing facilities and support a more reliable ferry service.'
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