It originates just a few kilometers from Lake Rėkyva near Šiauliai city in northern Lithuania.

The Dubysa has about 40 tributaries, the largest being Kražantė on the right and Šiaušė, Gryžuva, and Gynėvė on the left.

Dubysa is mainly fed by rainfall and melting snow, therefore its water levels change rapidly.

Dubysa is connected with the Venta River by the abandoned Windawski Canal started in 1825 by the authorities of the Russian Empire.

The intention was to connect the Neman basin with the Baltic Sea through the port of Ventspils.

After the war there was no purpose for the canal as Lithuania gained control over the Klaipėda region and lower reaches of Neman.