This winter’s plethora of precipitation has finally nudged the Sea of Galilee’s water level over its “bottom red line,” and the Israel Water Authority says the lake is the fullest it has been in the past four years.

Thus far, the winter of 2011-2012 has been a boon for the country’s dwindling water supply. Reflecting this, the level at the Sea, Israel’s most important source of drinking water, is now a full 113 centimeters above the recorded level this time last year. The water level in the lake rose above the bottom red line, -213 meters, this weekend, reaching -211.76 meters on March 18.

The closely-monitored level of the Sea of Galilee, the lowest freshwater lake on earth, is measured by a system of red and black lines. The upper red line is 208.8 meters below sea level, and has not been reached in more than a decade; when the lake reaches that level the Deganya dam is opened to prevent flooding around the lake.

The lower red line is 213 meters below sea level, and is a warning sign the lake is approaching a point where it could be dangerous to draw water. The bottom limit, the black line at 214.87 meters below sea level, indicates that water cannot be pumped without causing severe damage to Israel’s water supply.

However, even as Israelis celebrate the especially rainy winter and the rising water levels in the Sea of Galilee, a sobering report newly released by the Israel Water Authority said that the amount of rainwater reaching the lake has actually decreased by 11 percent over the last two decades.

The report, published by the Israel Hydrological Service at the Israel Water Authority, noted that an 11 percent decrease is significant over a period of two decades, during which the below-average rainfall impacted national water supply. The report predicts that regional water resources will continue to decrease in the future.

The Water Authority report focused particularly on the Sea of Galilee, which supplies some 30 percent of the country’s fresh water. Between 1950 and 1980, some 505 million cubic meters reached the lake on an annual basis; however, between 1980 and 2010 the annual average dropped to 385 million cubic meters. Levels could decrease an additional 15 percent in the two decades to come, the report claims.

The Eastern Mountain basin, which provides water to both Israel and the Palestinian Authority, also saw a decrease of average annual replenishment from 173 million cubic meters a year (1976-1992) to 138 million cubic meters (1993-2009).

The Water Authority released a report last month entitled “The Water Issue Between Israel and the Palestinians” which accuses the Palestinian Authority of failing to reuse wastewater, and not promoting sufficient water conservation.