Their comments were made in the hue and cry that followed a water retention basin in the southern province of Ba Ria-Vung Tau Province turning pink-purple late last month, exuding a foul smell and disrupting life in the area.

The basin is supposed to hold treated wastewater from nearby seafood processing factories, and to help regulate flooding during the rainy season. When its floodgates are opened, the water would typically flow towards the Rach Van and Cha Va rivers before reaching the sea, where hundreds of families engage in fishing and aquaculture.

The change in water color is being investigated. One company that discharged wastewater has been fined VND372 million ($16,160).

However, this is not the first time that such an incident has occurred. In 2017, an algae bloom triggered by pollution also changed the water color.

"It is not just a question of foul smell and strange color. We do not know what chemicals are discharged, which of these are creating the problem, and how dangerous they are," said Professor Asit Biswas of Scotland’s Glasgow University.

He suggested that authorities investigate this issue thoroughly to determine what the chemicals are and assess their long-term impacts on human and aquatic life.

Professor Hans Schreier of the University of British Columbia in Vancouver, Canada, said that to deal with water pollution problems, proper wastewater treatment is a must. Companies should be forced to send their effluents to a community treatment plant first for processing.

Biswas said water pollution is a problem in nearly all developing countries. There are often laws and regulations to control water pollution, but these are seldom enforced, he noted. Consequently, all water bodies near and within urban centers in all developing countries are heavily polluted with known and unknown pollutants.

Regarding the situation in Vietnam, he said that if the laws are not strong enough to prevent such practices, they should be strengthened. Vietnamese regulatory authorities should heavily fine seafood processing factories, especially their owners, including awarding long-term prison sentences. Corruption is another issue that needs serious attention in this context, he said.

"Unless sanctions allowed under law are strictly enforced, not much long-term improvements can be seen," he said.