Ciervo de los Pantanos National Park, National park in Buenos Aires Province, Argentina.

Ciervo de los Pantanos National Park is a protected reserve in Buenos Aires Province that combines wetlands, forests, and waterways in one place. The land sits near the Paraná River Delta where different natural habitats meet and support each other.

The land belonged to engineer Rómulo Otamendi (1852–1934), who received it as payment for railway surveying work. After his death it passed through several administrations and lay abandoned in the 1980s, when the national government transferred it to the National Parks Administration. Decree 2148/1990 created the Otamendi Strict Nature Reserve, and decree 453/1994 split the land into strict, wild and educational reserves. Law 27456 of 10 October 2018 made it a national park.

The park is named after Blastocerus dichotomus, the marsh deer, Argentina's largest deer and a declared natural monument. The species gave the protected area its name when the national park was created in 2018 from Otamendi and Río Luján reserve lands. The deer's presence in the Paraná Delta wetlands is the reason the area was granted national park status.

The park entrance is about 7 km from Campana and 69 km from Buenos Aires, reached by road. Trails cross wetlands and grassland, so wear waterproof footwear and carry rain protection. Frosts can occur between May and November.

The park protects 309 bird species, and about 70% of the Pampean region's birds occur here. Otamendi was declared a Ramsar wetland on 22 March 2008 and is also an Important Bird Area. The emblematic marsh deer, Blastocerus dichotomus, is South America's largest deer and a natural monument.