Barra do Una Sustainable Development Reserve, Nature reserve in São Paulo, Brazil.

Barra do Una is a nature reserve on the São Paulo coast that spreads across two municipalities where a major river meets the ocean. The area includes river channels, coastal waters, and forest sections connected as one protected zone.

The reserve was created by state law 12.406 of 12 December 2006 from part of the Juréia-Itatins Ecological Station, including the village of Barra do Una and part of the Una do Prelado River. That law was declared unconstitutional on 11 September 2007, confirmed on 25 June 2009, and law 14982 recreated the reserve within the Juréia-Itatins Mosaic.

The village of Barra do Una keeps caiçara festivals, traditions and costumes, maintained by its traditional inhabitants. The Associação Amigos de Bairro da Vila Barra do Una, founded in 2002, represents 45 families, about 120 people, and sponsors the RDS Community Sustainable Tourism Project to organise tourism in the reserve.

The reserve offers basic lodging options and outdoor activities like hiking and boat trips that are relatively easy to access. Wear sturdy footwear and expect changing weather conditions, since the location between river and ocean creates variable environmental conditions.

The Ilha do Ameixal Area of Relevant Ecological Interest covers an island in the Una do Prelado River just upstream from its mouth, beside the reserve. The reserve itself was carved out of the Juréia-Itatins Ecological Station by state law 12.406 of 12 December 2006, and the village of Barra do Una lies within it.