I've checked info. You are right. Boundary goes along old river channel. I will make corrections.

Hello. The access to the lake is closed to armenian citizens, except small part. I went to that lake and looked to the border fence and towers. I also lookes at google and yandex maps. But there can be error also. I am not sure. May be correct position of the border at the center of the lake, but border fence is at my line. I think we should display real situation of geographical and administrative objects in OSM. Thank you for your attention.

Большое спасибо. Хотел, но не догадался как. Век живи, век учись

Здравствуйте, спасибо что поправили. Что-то бес меня попутал :-)