Bird flu has been killing nearly 1,000 migratory cranes each day in Israel’s northern Hula Valley, according to local media.
Israel’s cranes “account for a tenth of the global population” of the long-necked birds, Haaretz daily reported.
It said around 40,000 cranes winter at the Hula Nature Reserve, and the ongoing epidemic threatens to kill a quarter of them.
Crane tourism is estimated to bring millions of dollars to the local economy.
Scenes of large numbers of dead cranes have appeared online, with at least 5,000 crane carcasses found this week at the Hula Nature Reserve, which has since been closed to the public.
Environment Minister Tamar Zandberg described it as "the worst blow to wildlife” in Israel’s history.
It is not yet known how the contagious virus identified as H5N1 entered the reserve, but Haaretz’s report blamed “excessive human intervention in nature” for the disaster, as the Hula Lake Park became a popular safari destination.
Tourists' attempts to feed cranes made the wild birds stay in the valley instead of taking their long traditional migration to Africa, according to ecologists.
This in turn caused overcrowding, making it easy for pathogens to spread.
At least seven tons of peanuts were fed to the cranes each day, Haaretz reported, with farmers paying for the nuts as a way of keeping the birds from raiding their fields.
“Intentionally or not, feeding by humans caused this,” Haaretz quoted one expert as saying.