Crews started the job Sunday, but a problem with the barge it was using for the work is delaying the repair.
The repair involves pulling the cable up from the bottom of the Northumberland Strait, laying it on a barge, cutting out the damaged section, and splicing in a new piece.
The barge is now in port and will stay there until it's fixed.
The company first discovered the leak in March when oil pressure in the cable started falling. It took some time to find the leak, and the company then had to wait for good weather to attempt the repair.
Since then, it found and fixed a second leak in another part of the cable that is above ground on the New Brunswick side. That repair cost $1 million, and the underwater repair is expected to cost $4 million.