Even though the Amazon River is over 4,000 miles long, there are good reasons why there are no bridges spanning it:

The Amazon, for much of its 4,300-mile (6,920 kilometers) length, meanders through areas that are sparsely populated, meaning there are very few major roads for any bridge to connect to. And in the cities and towns that border the river, boats and ferries are an established means of moving goods and people from bank to bank, meaning there is no real need for bridges to be built, other than to make trips slightly quicker…

For example, its extensive marshes and soft soils would necessitate “very long access viaducts [a multi-span bridge crossing extended lower areas] and very deep foundations,” and this would require hefty financial investment, Kaufmann said. Additionally, the changing positions of the river’s course across the seasons, with “pronounced differences” in water depth, would make construction “extremely demanding.” This is due, in part, to the river’s water level rising and falling throughout the year and the soft sediment of the riverbanks eroding and shifting seasonally, according to the Amazon Waters initiative (opens in new tab)…

Pontoons, or floating structures, are not a solution that would work in most parts of the Amazon, Kaufmann said, because the river is hugely impacted by seasonal variances, which adds an additional layer of complexity. For instance, during the dry season — between June and November — the Amazon averages a width of between 2 and 6 miles (3.2 and 9.7 km), while in the wet season — December through April — the river can be as wide as 30 miles (48 km), and the water level can be 50 feet (15 meters) higher than it is during the dry season, according to Britannica (opens in new tab)…

“I think a bridge would only be built if the need dominates over the difficulties and cost,” Kaufmann said. “Personally, I doubt that this will happen soon, unless there are unforeseen economic developments in the region.”

These are significant challenges, including engineering concerns and the lack of economic justification. Money always matters in big infrastructure projects as the costs can add up and the current system can be deemed okay and more cost-efficient.

So how might this change? I can imagine two scenarios:

1. A leader, political or otherwise, wants to make a big splash and attach their name to a significant civic project. Government officials often like this as infrastructure lasts a long time and is viewed as furthering the public good. Additionally, attaching their name to a significant structure means they can be recognized longer.
2. An architect or engineer or related firm wants to make a big splash. Perhaps the bridge is a unique design for the particular environmental conditions or perhaps it is especially green, particularly if there are fears that a bridge would negatively impact the environment.

In either case, to be part of the first bridge over the Amazon would be a notable achievement.