The river Gruda flowing in Alytus county, Varena district, Marcinkonys municipality, the river Merkys left tributary. Length of the river 45 km, the basin area 194 km ². The Gruda flows from the lake Grudas, near the Lithuanian - Belarusian border. Flowing through the forests to the north, in the lower reaches to the north west. Flows into the river Merkys 14 km from its mouth, at Puvociai village. Average gradient 95 cm / km. Average rated discharge at the mouth 1.88 m³/s.

All year.
Shallows, dam, strainers.
WW 0. Section below village Kirklys WW 1+

27.2 Marcinkonys - Margionys road bridge. Darzeliai. Average discharge 1.20 m³/s. Average gradient to the brook Dorupis 83 cm/km. The average width of the river about 5 m. The first 3.8 km river channeled, flowing through the forests.
23.4 Channeled river section ends. The river very meanders, flowing through the forests. Footbridges, In the riverbed can be strainers.
20.8 right Dorupis. right Marcinkonys. Average gradient to Kasetos village 67 cm/km.
18.9 Marcinkonys - Rudnia road bridge. right Marcinkonys.
12.4 Marcinkonys - Puvočiai road bridge.
10.6 right tributary from the lake Versminis. Average gradient to the mouth 204 cm/km.
6.6 The wooden bridge. left Kasetos. At the village a lot of low footbridges.
5.4 Bridge.
3.3 left Kirklys (uninhabited). Below the village the Gruda begins to descend into the valley of the Merkys river. Gradient above 5 m/km. To the mouth in the riverbed small rapids, current fast. The width of the river 7-10 m. At low water level this section of the river is too shallow.
0.0 The Gruda flows into the river Merkys. 50 m before the mouth the wooden bridge. left Puvociai.