Hello, after studying pages after pages 
of
official documents concerning this 
border
I proudly report this:
Yes, since 1816 - the year of the first 
written
agreement on the boundary line between 
the
Kingdoms of the Netherlands and Prussia 
-
all water bodies forming the boundary 
lines
between these 2 countries are to be 
considered
as "condominiums" ... many attempts have 
been
made in the meantime, however, to change 
the
status of the boundary line, untill today with 
no
result. The latest agreement between 
Lux&Ger
was signed in 1984 and contained no 
adjustment
regarding the river boundaries....
So, I think we can now establish this as a 
fact:
The Ger-Lux boundary line, mostly 
consisting
of rivers like Mosel, Sauer and Our are in 
the
possession of both states...
Kind regards
Peter