. The tributaries, in order going upstream, are Kushum, Derkul, Chagan, Irtek, Utva, Ilek (major, left), Bolshaya Chobda, Kindel, Sakmara, Tanalyk (major, right), Salmys, Or (major, left) and Suunduk. The Kushum is a distributary. The entire length of the Ural River is considered the Europe-Asia boundary by most authoritative sources. Rarely, the smaller, shorter Emba River is claimed as the continental boundary, but that pushes "Europe" much further into "Central Asian" Kazakhstan. The Ural River bridge in Orenburg is even labeled with permanent monuments carved with the word "Europe" on one side, "Asia" on the other. Regardless, Kazakhstan has some European territory and is at times included in European political and sports organizations. Hydrography The river is mostly fed by melting snow (60–70%); the contribution of precipitation is relatively minor. Most of its annual discharge (65%) occurs during the spring floods, which occur in March and April near the mouth and in late April through June upstream; 30% drain during the summer and autumn and 5% in winter. During the floods, the river widens to above near Uralsk and to several tens of kilometers near the mouth. Water level is highest in later April upstream and in May downstream. Its fluctuation is in the upper stream, in the middle of the river and about in the delta. The average water discharge is near Orenburg, and at the Kushum village, which is from the mouth. The maximum discharge is and the minimum is . Average turbidity is at Orenburg and near Kushum. The river freezes at the source in early November and in the middle and lower reaches in late November. It opens in the lower reaches in late March and in early April in the upper reaches. The ice drift is relatively short. The average depth is near the source, and it increases in the middle reaches and especially near the mouth. The density of underwater vegetation also increases from the source to the mouth, so as the richness of the fauna. The bottom in the upper stream is rocky, with pebble and sand; it changes to silt-sand and occasionally clay downstream. The basin is asymmetrical – its left side from the river is 2.1 times larger in area than the right side; however, the right side is more important for feeding the river. The density of the tributaries is 0.29 km/km2 in the right and 0.19 km/km2 in the