Scottish Water admits it has not established the cause of a burst mains sewer in the centre of Ayr.
Engineers are currently tackling the problem at the town's harbour.
But the water authority admits it could be weeks before they complete "complex" repairs.
They have pledged to launch a "full investigation" into the rupture which happened by the water's edge.
Specialist contractors are working on the 1100mm trunk main, with part of South Harbour Road closed.
The incident had caused "minimum damage to the environment," they said.
Tide levels will now determine how quickly the repair takes place.
A spokesperson said: "Our main priority is to carry out a permanent repair to the sewer and restore normal service to the area for our customers.
"A full investigation will be carried out to establish the cause of the issue to the sewer and determine the full scope of any further works.
“This is a complex repair, due to the location and the remedial works which are required.
"We would like to reassure customers that the environmental impact has been minimal, and the health and safety of those living, working or visiting the area remains paramount.
“We apologise for any inconvenience caused and thank everyone for their patience while these essential works are completed.”
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