Israel has pledged to release about 1 billion cubic feet of water to restore the biblical Jordan River.
Israel, Syria and Jordan have diverted nearly all of the river's fresh water. The trickle that remains is mostly raw sewage.
Last year, Israel began building a $106 million complex to remove the sewage water and treat it for agricultural use. But that would have left the river dry.
In a statement, Environment Minister Gilad Erdan promised to start replacing the sewage with clean water in 2013, saying it will "allow life to return to the river."
Environmentalist Gideon Bromberg said the promised amount is less than a 10th of what is needed to fully restore the river.
"It's a first drop, but it's an important drop," Bromberg said.