The river Seira flows in Alytus county, Lazdijai district, the river Baltoji Ancia left tributary. Length of the river 48 km, the basin area 222 km ². The source 7 km northeast from Seirijai town. Flows to south through the lakes Sagavas, Seirijas and Krastas. To the lake Sagavas calls Sarkiske, betveen the lakes Sagavas and Seirijai calls the Sagavas. The Seira flows into the river Baltoji Ancia 5 km from its mouth, 11 km southwest from Druskininkai town. Average gradient 129 cm/km. Average rated discharge at the mouth 1.42 m³/s.

All year.
Strainers.
WW 0 (1-).

19.6 Bridge. left Leipalingis. Average gradient the Baltoji Ancia pond 31 cm/km. The river width 5 m. The current calm. Can be stariners, fallen trees, beavers dams.
18.2 right Vilke flows from the lake Vilkine. The river widening up to 5-7 m. The river flows through forests.
17.7 left Simaniske.
14.9 right the brook S-2.
11.1 left Vilkanasriai.
9.2 Bridge. ridht Dulgininkai.
6.9 Begins the Baltoji Ancia pond. The pond looks like wide river (width 30-150 m ). At the banks forests.
5.0 right Dulgele flows from the lake Dulgas.
0.0 The Seira flows into the river Baltoji Ancia.