A defense factory spill of a deadly cyanide compound has poisoned Latvia's main river, killing 300,000 fish and leaving one-third of the capital of Riga without water, officials said.

The chemical acetone cyanohydrin gushed from the plant in the republic of Byelorussia for 15 hours last week into the Western Dvina River in an ecologocial disaster that will have lasting effects, Janis Peters, chief of the Latvian Mission in Moscow, said Tuesday. The cause of the spill was not known.A videotape viewed by reporters at the Latvian Mission showed droves of fish leaping from the water and dying on the banks of the river in the Latvian city of Jekabpils.

Peters said the disaster has caused $34 million in direct economic damage and up to $510 million in indirect damage such as lost work time.