Dead fish float on the surface of West Lake, giving off a foul smell

Recorded on the afternoon of August 26, in the West Lake area along Nguyen Dinh Thi, Trich Sai, Thanh Nien streets...mass dead fish washed ashore.

Although sanitation workers are still actively scooping and cleaning up, there are still many dead fish drifting ashore, giving off a foul smell.

Immediately after the mass fish deaths, the People's Committee of Tay Ho District coordinated with the Department of Construction to direct the Hanoi City Technical Infrastructure Management Center (Department of Construction) to urge the Hanoi Drainage Company Limited to monitor, inspect and increase the collection of dead fish to ensure the environment and urban beauty.

Currently, Hanoi Drainage Company Limited is increasing the collection and transportation to the treatment site according to regulations; the average collection quantity is 50kg/day, the dead fish are mainly carp, silver carp...

Speaking to VietNamNet, Mr. Nguyen Dinh Khuyen, Chairman of Tay Ho District People's Committee, said that recently, fish deaths have continued to occur in the West Lake area. The cause may be due to rain and water flowing from other places, polluting the lake, leading to mass fish deaths...

Mr. Khuyen said that the results of water source monitoring are still at the permissible level, not reaching the dangerous threshold. The district has directed the collection and disinfection to treat the environment in the area where the dead fish were collected.

Dead fish have washed up on the shores of West Lake in recent days, giving off a foul smell.

Hanoi Drainage Company Limited is increasing collection and transportation to treatment sites according to regulations.

Explaining the phenomenon of dead fish in West Lake, Associate Professor Vu Thanh Ca, senior lecturer at the Faculty of Environment at the Hanoi University of Natural Resources and Environment, said that normally during the changing seasons, around September and October, the sun is in the Southern Hemisphere, so the amount of sunlight during the day reaching the ground and water surface is low.

At night, the lake surface and ground cool very quickly, making the air layer below colder, creating a temperature inversion phenomenon.

The temperature inversion phenomenon will prevent oxygen exchange between the air layer near the lake surface and the air layer above.

There have been many cases of mass fish deaths in West Lake.

On inversion nights, organic decomposition from untreated wastewater and respiration of planktonic algae in the lake rapidly deplete oxygen in the water.

The amount of oxygen in the air layer near the lake surface will also be quickly depleted because the air layers above cannot continue to diffuse oxygen into the water. As a result, oxygen depletion will occur throughout the entire water column, causing mass fish deaths.

"According to the results of the daytime measurement by the Hanoi City inter-agency, we see that the oxygen concentration is still guaranteed, but it is incorrect to conclude that the oxygen concentration is guaranteed but the fish still die. In all cases of mass fish deaths in the world, people concluded that it was due to oxygen depletion.

"If we want to find the cause of the fish deaths in West Lake, we have to measure the oxygen concentration at night, from around midnight to morning," Associate Professor Vu Thanh Ca said.

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