>IMHO this is a Vasco-Caucasian loanword from NEC *järKwi:/*Kwä(j)ri: (~ -e:) 'sea', where /K/ represents the voiceless fricative lateral. The metathesized root is found in Celtic *liro- 'sea, ocean'.
> > Have anybody thoughts about Baltic jura - the sea. Also in Baltic
> > territory are some hydronyms: rivers Jara, Jura and etc...
> Finnish, järvi is probably from this source.
> Lithuanian, jáura (swamp).
> The rest I'll leave to others with some real knowledge.