Five Uruguayan islands inside Argentine territorial waters. Filomena Grande is the largest in a group of islands in the Uruguay River belonging to the Oriental Republic of Uruguay and which form the country's territorial exclaves surrounded by waters of the Province of Entre Rios in Argentina. Administratively part of the Department of Río Negro. Sovereignty over the islands was in dispute until 1961.

The islands are making five enclaves/exclaves as the Uruguayan land is completely surrounded by foreign (Argentine) territory (inland waters); Filomena Grande I., Filomena Chica I., Palma Chica I., Bassi I. and Tres Cruces Island.  All islands appear to be uninhabited.  The Argentina-Uruguay boundary has been delimited from the Brazilian tripoint to the parallel of Punta Gorda by the Uruguay River Treaty ⁴⁾ signed in 1961 and ratified in 1965. ^{1, 3)}  

From the area of the bifurcation of the Filomena and El Medio channels to the area where these channels join, the boundary divided into two lines. One boundary line coincides with the Filomena channel and divides jurisdiction over waters. The other line coinsides with El Medio channel, dividing jurisdiction over islands, and represents the sovereignty boundary. [Inset 7]

The three western islands are now situated very close to each other, but they were in 2011 still separated from each other.

Sources

1.  From Attachment "Argentina-Uruguay Boundary" (53648 6-66), Office of the Geographer, Department of State, USA.

2. Cropped Inset 7 from Attachment "Argentina-Uruguay Boundary" (502678 8-75), Office of the Geographer, Department of State, USA.

3. Spanish Wikipedia (Spanish): http://es.wikipedia.org/wiki/Isla_Filomena_Grande

4. Tratado del Río Uruguay (1961) (Spanish): http://es.wikisource.org/wiki/Tratado_del_Río_Uruguay_(1961)