The paper analyses groundwater flows in the Orontes River basin and the changes which occurred in the past forty years as a result of the massive expansion of irrigated lands using groundwater resources in the Orontes River basin. The region contains significant karstic water resources supplying springs in the upper and middle reach of the basin. Although variations in annual flows are difficult to access precisely, there was a significant decrease since the 1960s. The Syrian Lebanese agreement on the sharing of the Orontes water signed in 1992 focused almost exclusively on surface water resources. The drilling of wells in Lebanon was restricted only nearby the Orontes River bed. Amendments to the agreement, in 1997 and 2002, restricted the drilling of wells in the Lebanese section of the basin as a whole. However no restrictions were imposed on groundwater withdrawals in Syria. Because of the continuity of the main Jurassic-Cretaceous aquifer between the two countries the latter withdrawals are likely to affect groundwater resources in Lebanon.