A total of 1,622 bodies of wild geese, as well as more than 50 dead fish, found on the shores of Lake Ubsu-Nur in the Republic of Tuva on the Russian-Mongolian border had been incinerated by Monday.
After preliminary tests, local virologists suggested bird flu had caused the mass bird deaths in the last week, but Vladimir Zabelin, a leading local ornithologist, said contamination of a river flowing into the lake could have been to blame.
"[The deaths] could have been the result of toxic waste being dumped into the Tes-Khem River," he said.
The expert said the fish started dying first, apparently contaminating the birds through the food chain.
The final results will be known by June 29, when a Vladimir-based research institute in central Russia finalizes the analysis of blood samples from dead birds.