As locals and tourists took pictures and videos of the disturbing scenes and shared them on social media, officials said this would happen again till the city completes a wastewater drainage and treatment project by the end of this year.
The wastewater came from the My Khe coastal drainage system in Ngu Hanh Son District, local reports said.
To Van Hung, director of the Da Nang Department of Natural Resources and Environment, explained that as soon as rain was forecasted in the city, the Da Nang Drainage and Wastewater Treatment was asked to collect all the wastewater left in its drainage system.
"When it rains heavily, the wastewater has to be expelled. The water is black at first, as seen in the video locals have recorded, but after a while, it becomes clearer when diluted by rainwater," he said.
Wastewater pouring out to sea when it rains is a common scene on the Da Nang coast. The city’s drainage systems now collect both rainwater and wastewater, and when the system is flushed out by rainwater following a downpour, untreated wastewater gets mixed.
The coastline in Ngu Hanh Son and Son Tra Districts has at least nine drainage systems that dump untreated wastewater straight into the sea.
Da Nang is currently implementing a project that would construct more drainage systems along the eastern coastline of the districts. The VND2.45 trillion ($105.6 million) project is expected to be completed this year.
Until then, the situation of untreated wastewater pouring out to the sea is likely to recur, said Hung.