The Amazon is the major river with no bridge crossing its entire main stem. Although the river is enormous, its lack of a full-width bridge is mainly a consequence of geography and infrastructure rather than an impossible engineering challenge.
Much of the Amazon flows through rainforest with relatively few roads, large towns, and fixed transport links. Ferries therefore remain the usual way to cross it. The river also spreads into multiple channels and floodplain areas, making a single bridge route difficult to plan and maintain.
A common mix-up involves the Manaus–Iranduba Bridge, which opened in 2011. That bridge is often described as an Amazon crossing, but it spans the Rio Negro, one of the Amazon's largest tributaries, just before the rivers meet. It does not cross the Amazon's main stem.
The Amazon proper runs mainly through Brazil and Peru and drains one of the world's largest river basins. Its main channel can be relatively narrower in places than popular photographs suggest, but the surrounding wetlands, islands, seasonal flooding, and limited road network remain formidable obstacles.