Isla Demarchi, Industrial island in La Boca, Argentina.

Isla Demarchi is the northeastern sector of La Boca, in Buenos Aires, often mistakenly considered part of Puerto Madero. It holds shipyards, port warehouses, the Costanera power plant inaugurated in 1966, the Naval Observatory, the Museo de Calcos, and the former Ciudad Deportiva de Boca Juniors.

What began as a sandbank near the Riachuelo was purchased in the 19th century by Antonio Demarchi and his brothers, who transformed it into an industrial zone. This development made the island a key center for port and naval operations.

The island's name comes from the Demarchi brothers, Antonio, Marcos and Demetrio, sons of the Italo-Swiss baron Silvestre Demarchi, who owned the land when it was filled in the early 20th century. River Plate played its first, makeshift pitch here behind the Wilson coal yards. The former Ciudad Deportiva de Boca Juniors also occupies part of the island.

The area is used by port and naval authorities and private companies, making it not readily accessible for casual visitors. A visit typically requires permission or participation in guided tours offered by local organizations.

The National Naval Arsenal, established in 1879, continues to operate and maintains Argentine Navy vessels on the island. This historic facility makes the site an important military and technical center.