The river Asva flowing in Akmene and Mazeikiai districts, the river Vadakstis left tributary. Length of the river 33 km, the catchment area 172 km ². Source in  Kamanai swamps, 7 km to northwest from Vieksniai town. Flowing to northwest, crosses Mazeikiai - Jonava railway. Flows into the river Vadakstis 3 km from its mouth. In upper section of the river valley wide, shallow, marshy, in lower section the valley narrow and deep. Average discharge at the mouth 1.38 m³ / s, max. 40 m³ / s.

At higher water level. Spring, or after heavy rains.
Shallows, rapids, stariners, dam.
WW 1- (1+).

8.4  Tulnikiai dam. Height 5 m, the pond area of 29 hectares. Average gradient to Kulupis river 135 cm / km. To the mouth of the river flows through forests, valley deep, steep banks, height up to 12 m. Outcrops. The river current is fast, rare  small rapids, strainers.
6.8 Bridge. right Tulnikiai.
5.7 left Osupis.
4.4 right Alksnupis.
3.3 left Mantvydai.
2.4 right Kulupis. The current calm, the Leckava pond begins.
0.7 Leckava HPP dam. Height  7 m, the pond area 12 hectares. left Leckava. Average gradient to the mouth 171 cm / km.
0.0 The Asva flows into the river Vadakstis.