This looks like being a real condominium. See
http://www.dams.org/submissions/sub_sp_filho_en.htm :

"ITAIPU Binacional. This binational entity was formally constituted
on May 17, 1974, and is co-owned by both countries, which
participate, in equal proportions, in the capital of the enterprise
through Centrais Elétricas Brasileiras S.A. ELETROBRÁS of Brazil
and Administración Nacional de Electricidad - ANDE of Paraguay. On
account of being one entity endowed by two governments with the
powers to own, build, and operate, on their behalf, a hydroelectric
power plant on a river owned in condominium by the two countries
involved, Itaipu Binacional has a quite particular legal standing
under international law."

&

"(...)the negotiations that took place between the Governments of
Brazil and Paraguay and culminated in the signature, on March 16,
1973, of the Itaipu Treaty for the hydroelectric development of the
stretch of the Paraná river belonging in condominium to both
countries (...)"

Peter S.

--- In BoundaryPoint@y..., "Peter Smaardijk" <smaardijk@y...> wrote:
> Acc. to
> http://www.internationalwaterlaw.org/RegionalDocs/Parana2.htm
>
> Peter S.