A recent series of tides over 2.2m meant salt and stormwater had been flowing back up the pipes from Otago Harbour and on to the two streets, near their intersections with Portsmouth Dr.
Concerned Dunedin boatie Martin Balch said people needed to be aware they were driving through salt water and spreading salt residue down both streets and Portsmouth Dr, which was not good for their cars or road conditions.
Tides had been at spring high tide level for the past nine days and low barometer pressures were pushing the tides even higher. The high tide on Sunday night reached 2.5m and yesterday at about 12.30pm 2.4m. This was expected to continue for the next few days.
Dunedin City Council road maintenance engineer Peter Standring said when the high tides coincided with wet weather, stormwater was not flowing into the harbour but going back up the pipe.
In drier conditions, when the tides hit about 2.2m it was salt water coming back up the pipes and on to the roads.
"Our biggest concern is people hitting flood water at speed in the dark."
The main cause of the problem was that reclaimed land was continually consolidating and at its worst point had dropped 500mm, he said.
In the short-term the council was considering installing more signs to make people aware they could strike flood water unexpectedly in those areas.
Installing back-flow preventers in the pipes, to prevent sea water from coming up the pipes, was being investigated and in the longer term, the council could look at capital works, such as raising the level of the road, he said.
