Companhia Brasileira de Navegação do Rio Amazonas - This name can be translated as "Brazilian Company of Navigation of the Amazon River." The flag is white containing a couple of anchors disposed in saltire.
This is now the Pará-state-owned Empresa de Navegação da Amazônia, S.A. (ENASA), using the same flag. Viewable at the company website, in the upper left corner of the page.
ENASA is owned by the state of Pará and serves Amazon river ports between Belém and Manaus. It was founded in 1852 as the Companhia de Navegação e Comércio do Amazonas, a private firm subsidized by the imperial treasury. In 1872, it was sold to British investors and became the Amazon Steam Navigation Co., Ltda., still subsidized by the imperial government as a means of developing the Amazon hinterland. The Brazilian federal government nationalized the company in 1940 and combined it with the port authority of Belém and other ports in Pará to become the Serviço de Navegação e Administração dos Portos do Pará, or SNAAPP. SNAAPP was broken up in 1967, with the state ports authority becoming separate from the shipping line, which was renamed ENASA.