The world's 'largest' river that doesn't have a single bridge across it - for 2 reasons

The Amazon River in is the largest river by discharge volume of water in the world and battles with the Nile in Africa for the title of the longest in the world, at an impressive 4,300 miles. It is one of the world's most significant waterways, stretching across Peru, Colombia and .

It is home to the world's largest species of river dolphin and some 60 species of piranha. However, despite all these incredible stats, there is something that cannot be found on the Amazon - bridges. This seems strange, considering more than 30 million people live in the river's basin, according to the .

Over in Egypt, there are nine bridges that span the in Cairo alone. Meanwhile, the Danube, which is only around a third as long as the Amazon, has an incredible 133 bridge crossings.

"There is no sufficiently pressing need for a across the Amazon," said Walter Kaufmann, chair of Structural Engineering (Concrete Structures and Bridge Design) at the Swiss Federal Institute of Technology (ETH) Zurich, according to .

Despite its impressive length, much of the Amazon passes through areas that are sparsely populated, meaning there are very few major roads.

In cities and towns that border the river, boats and ferries are utilised to move goods and people from each side, meaning there is no real need for bridges to be built.

There are also technical and logistical difficulties, Kaufmann added. Its extensive marshes and soft soils would require "very long access viaducts [a multi-span bridge crossing extended lower areas] and very deep foundations," he explained, all which would require substantial financial investment.

On top of this, the Amazon also changes its course throughout the year, with "pronounced differences" in water depth, which would make construction "extremely demanding".

According to the , the river's water level rises and falls throughout the year and the soft sediment of the riverbanks erodes and shifts seasonally.

While these are not issues unique to the Amazon - they are "particularly severe" here, added Kaufmann. During the dry season - June to November - the amazon averages a width of between two and six miles, while in the wet season, the river can increase to some 30 miles wide and the water 50 feet deeper than during the dry season, according to .

"The environment at the Amazon is certainly among the most difficult [in the world].

" across straits are also challenging if the water depth is deep, but at least you know that construction is possible using pontoons, for example."

For now, there is no need to build a bridge across the Amazon, which will come as a relief to its South American countries, as they will have to fork out some considerable costs to make it happen.