Sejny
It is located in the eastern part of the Suwałki Lake Area , on the Marycha river ( "Seina" in Lithuanian for which the town was named ) , being a tributary of the Czarna Hańcza . 
<triplet> Marycha <subj> Czarna Hańcza <obj> mouth of the watercourse <triplet> Czarna Hańcza <subj> Marycha <obj> tributary