The Bega is a 254 km long river in Romania (178 km) and Serbia (76 km). It rises in the Poiana Ruscă mountains in Romania, part of the Carpathian Mountains, and it flows into the Tisza river near Titel, Vojvodina, Serbia.

The river starts at the junction headwaters: Bega Luncanilor and Bega Poieni. After starting of to the north, river bends to the west at Coşava, passing through Făget, Balinţ and Topolovăţu Mic, where it enters the low Banat plains. There, it begins to spill over, so the Bega canal was constructed tracking Bega Veche, which is also channeled for 97 km, as parallel waterway for 114 km, before the two being connected northeast of Zrenjanin, Serbia. The Bega canal runs through Timişoara and continues to the south-west, enters Serbia near the village of Hetin.

Near Jankov Most the Begej becomes part of large canal Danube-Tisa-Danube (or DTD) and turns south, receiveng waters from Novi Begej. There it's separated from DTD route turning west and reaching Zrenjanin. From there it continues to the south, using old river bed of Tisa, passing through Ečka, Stajićevo and Perlez. In this part, it flows through marshlands, some of which are transformed into fishponds, like Belo jezero (Cyrillic: Бело језеро; White lake) and Fishpond Ečka (Serbian: Ribnjak Ečka, Рибњак Ечка), the largest one in Serbia with an area of 25 km². The remaining parts of wetland make the largest bog in Serbia, Carska bara (Cyrillic: Царска бара; Imperial marsh, 11 km²), after which Begej empties into the Tisa.

Through Tisa and Danube, it belongs to the Black Sea draining basin. Its own draining area is 2.878 km².

Channeled parts of both Stari Begej and Novi Begej are navigable.

Settlements on Novi Begej include villages of Srpski Itebej (with huge fishpond), Novi Itebej, Torak (formerly Begejci) and Žitište.