The problem has been seen at some beach sections stretching around three kilometres through the city centre.
Many tourists encounter oil lumps, which are quite difficult to clean.
This is not the first time such oil clumps have been reported in Nha Trang.
The phenomenon might have been caused by offshore vessels discharged and brought ashore by the currents. Nha Trang Urban Environment Joint Stock Company has arranged for 20 workers to clean up the oil.
The Nha Trang Bay Management Board has warned residents and tourists to be cautious when swimming in areas affected by oil clumps.