The river Seimena flows in Marijampole county, Vilkaviskis district, the river Sirvinta (Senasirvinte) right tributary. Length of the river 48 km, the basin area 656 km ². The source at Budvieciai village, 15 km southeast from Vilkaviskis town. Flows to northwest. The Seimena flows into the river Sirvinta 6 km from its mouth, 5 km southwest from Kudirkos Naumiestis town. Average gradient 209 cm/km. Average rated discharge upstream the mouth of the river Sirvinta 1.27 m³/s, at the mouth 3.68 m³/s.

All year. Better at higher water level.
Strainers.
WW 0 (1-).

20.5 Virbalis - Zalioji road bridge. Andriskiai. The river meanders through swampy meadows, widh 3-5 m. Current calm. Average rated discharge 1.1 m³/s. The banks low, overgrown by rare bushes.
16.7 left Sirvinta. The river discharge more than doubles, the current accelerated, the river widening up to 7-10 m. Average gradient to the brook Juodupe 70 cm/km. The banks overgrown by trees, can be strainers.
15.3 Bridge. left Sukliai.
11.7 left Vilkupis. right Parazniai. left Vilkupiai.
8.7 Kybartai - Kudirkos Naumiestis road bridge. right Keturkaimis. left Peletrūnai. The river flows through meadows, at the banks rare bushes. Can be a few strainers.
6.7 left Juodupė. Average gradient to the mouth 33 cm/km. The current calm.
5.7 Bridge. right Lauckaimis.
3.0 left the brook S-1. The banks bare. No strainers. Before the mouth the river widening up to 15 m. The Seimena flows Lithuania - Russia border.
0.0 The Seimena flows into the river Sirvinta (Senasirvinte).