They have been heavily polluted by large quantities of industrial waste discharged every day for many years, says Ky Quang Vinh, director of the observation and testing center under the Can Tho Department of Natural Resources and Environment.

A pipe that discharges wastewater from a fishing farm directly to a canal in Can Tho.

“In a few years, Can Tho rivers and canals will be dead just like the Thi Vai River,” Vinh said as going to visit the rivers with Tuoi Tre this month.

The Tham Tuong Canal that runs into the Can Tho River has turned black and the canal bed has filled up with dense wastewater.

Thai Phuong Vu from the environment testing center said it’s now hard to get into the canal, unlike five years ago.

Vu also said there was no dissolved oxygen in the canal to measure.

According to Vinh, the level of dissolved oxygen (DO) – which is measured in standard solution units such as milliliters of O2 per liter (ml/L) – is “the most persuasive evidence” of a polluted river.

“If the level is 6, the river is considered alive. Below that, sick or weak. And if it’s below 1, the river can be seen as dead.”

The Sang Trang Canal, located 15 kilometers upstream of the Hau River, receives wastewater from hundreds of factories in the Tra Noc Industrial Zone.

The DO was first measured at 6 on the Hau River but deeper into the canal, the level dropped to 4, 3 and stopped at 2. Vu said the level is zero during the dry season like the months of March or April. “It’s always below the permitted level.”

Industrial wastewater, which is discharged by two big pipelines into the canal, would then flow into the Hau River that runs through different provinces of the Mekong Delta.

The 30-kilometer Thot Not Canal, connected to the Hau River, shows DO levels of 3 where there are markets on the banks and 2 where the banks are highly populated.

Tam, another environment officer in the city, said water discharged from tra catfish farms also added to the pollution.

The Dung Canal receives pesticides and weed-killer leftovers as many locals along the banks breed catfish.

The Thi Vai River in Dong Nai Province neighboring Ho Chi Minh City was last year found to have been contaminated with up to 105.6 million liters of untreated wastewater per month for over 14 years by monosodium glutamate maker Vedan.

Local farmers have blamed the toxic water for killing their fish and shrimp and ruining farmland along the river banks.