Otamendi natural reserve, Nature reserve in Buenos Aires Province, Argentina.

Otamendi natural reserve is a wetland area in Buenos Aires Province where the Pampas plains transition into the Paraná River delta ecosystem. The land supports both freshwater and saline environments that create distinct habitats within the same space.

The land belonged to engineer Rómulo Otamendi (1852-1934), who received it as payment for surveying railway layouts in Argentina. After his death it passed through several administrations and lay abandoned in the 1980s, when the national executive transferred it to the National Parks Administration. Decree 2149/1990 of 10 October 1990 created the Otamendi strict nature reserve on land of the National Council of Minors and Family in Campana district; decree 453/1994 of 24 March 1994 split it into strict, wild and educational categories. In December 2017 the Buenos Aires legislature passed law 15006 transferring 3,000 hectares to form Ciervo de los Pantanos National Park.

The reserve's name honours engineer Rómulo Otamendi (1852-1934), who traced railway layouts in Argentina and received these lands as a reward; his property was later bequeathed and, after passing through several administrations, stood abandoned in the 1980s. The educational category created in 1994 gives the reserve an explicit role in environmental education and interpretation of nature. Its management is headed by a superintendent based in the Otamendi neighbourhood of Campana.

Access is via RN 9 Panamericana to the town of Ingeniero Rómulo Otamendi, between Campana and Belén de Escobar; from the town's central street, the reserve entrance is 2 km on. By train, take the Mitre line from Retiro Mitre to Ingeniero Otamendi station, changing at Villa Ballester.

The reserve's land came from engineer Rómulo Otamendi (1852-1934), who received it as payment for surveying railway routes in Argentina. His estate was later abandoned, and in the 1980s the national government handed it to the National Parks Administration, which led to protection in 1990.