Río Abajo is a barrio in the municipality of Humacao, Puerto Rico.

[3][4][5] Río Abajo was in Spain's gazetteers[6] until Puerto Rico was ceded by Spain in the aftermath of the Spanish–American War under the terms of the Treaty of Paris of 1898 and became an unincorporated territory of the United States.

In 1899, the United States Department of War conducted a census of Puerto Rico finding that the population of Río Abajo and Mambiche barrios was 1,289.

In 2019, updated flood zone maps show that because of its location- where many hurricanes enter the island, Humacao is one of the most vulnerable areas of Puerto Rico.

[13] Humacao was working on flood mitigation plans and shared that its barrios located on the coast; Antón Ruíz, Punta Santiago, Río Abajo, Buena Vista and Candelero Abajo barrios, are prone to flooding and in danger of being completed destroyed by a hurricane.