Israeli media quoted the National Water Authority as saying on Sunday that the lake's level had fallen by 6 centimeters during the April 19-27 Passover holiday.
The level is expected to sink below the "black line", beyond which water cannot be drawn out, in July.
National authorities say the falling water level has been caused by a series of dry winters and the country's excessive water consumption.
To meet the national water needs, authorities plan to enforce water saving measures and pump greater volumes from underground aquifers.
Plans for new desalination plants are also in place.
Two large desalination plants provide around 30% of the country's water supply, and three more are scheduled for construction over the next five years.
