while the sandbank looks like a very long, very thin peninsula, it is in fact separated from the mainland by the canal do bacalhau - making of it an island - reason why the official name is ilha da marambaia (marambaia island). 

this canal, home the the island of bom jardim and part of the reserva biológica e arqueológica de guaratiba (renamed  reserva biológica estadual de guaratiba) borders the northern side of the marambaia, and is in itself a natural treasure.

marambaia is jointly administrated by the brazilian navy and the army, at it is used by all branches of the brazilian armed forces for numerous purposes, such as for military training and arms experimentation, chiefly by the marine corps.

the centro de adestramento da ilha da marambaia (cadim) has been operating there since 1981.