Qaraoun, Lebanon — Tons of dead fish have washed up on the shore of a highly polluted lake in eastern Lebanon in the past few days, an official said Thursday. It was not immediately clear what caused the fish kill in Lake Qaraoun on the Litani river, which several local fisherman said was unprecedented in scale.
A preliminary report said a virus had killed only carp in the lake, but a veteran water expert said their deaths could also have been caused by pollution.
Hundreds of fish of all sizes lay dead on the banks of the more than three-mile long lake on Thursday, and the stench of their rotting flesh clung to the air.
Men shovelled carcasses into a wheelbarrow, as a mechanical digger scooped up more into the back of a truck.
"It's our third day here picking up dead fish," said Nassrallah el-Hajj, from the Litani River Authority, dressed in fishing waders, adding they had so far "carried away around 40 tons."
On the water's edge, 61-year-old fisherman Mahmoud Afif called it a "disaster," and said he'd "never seen anything like it" in his lifetime.
Lake Qaraoun was built as a reservoir on the Litani river in 1959 to produce hydropower and provide water for irrigation.
But in recent years experts have warned huge quantities of wastewater, industrial waste, and agricultural runoff containing pesticides and fertilizer flooding into it have made it increasingly toxic.
Since 2018 fishing has been forbidden in the reservoir as the fish there were declared unfit for human consumption, though fish from the lake have continued to appear in several markets.
The Litani River Authority and the Society for the Protection of Nature in Lebanon on Friday warned of a "viral epidemic," and called for fishing to be forbidden in the Litani as well as in the lake.
It said the likely disease had only affected carp, while four other types of fish appeared to be unaffected.
Kamal Slim, a water expert who has been taking samples of water from the lake for the past 15 years, said pollution could also be the cause.
"Without analysis, we cannot be decisive," said the researcher.
But the lake is also home to cyanobacteria, or blue-green algae, and in warmer months the excess nutrients from pollution have caused the bacteria to erupt into bright green blooms that release toxins.
"Right now there is a cyanobacteria bloom, though less thick than last year," he said.
That or a bacteria could be responsible for harming the fish, especially since they are weaker during the reproduction season.
"Another possibility is very toxic ammonium," Slim said.
In July 2016, Lebanese media reported that tons of fish had floated to the surface of Lake Qaraoun overnight.
Slim said that was due to a toxic bloom and oxygen depletion.