Amazon River, Brazil

The world's mightiest river, the...

Amazon flows for 4,007 miles from the top of the Peruvian Andean Mountains into the Atlantic Ocean. The Amazon River is the world's largest river in volume of water - holding as much as all of the next 10 largest rivers in the world combined - pouring 8 trillion gallons of water into the ocean every day, and the second in length. The Amazon River holds 20% of all of the fresh water on the planet. The Amazon's width is of 120 miles when it meets the Atlantic, and its average depth is of 50 ft. Many of the world's top 20 largest rivers, including the Rio Negro, flow into the Amazon. The rare pink dolphin and a diversity of fish species inhabit the mighty waters of the Amazonian rivers.

The estuary of the Amazon is about 330 kilometres (205 miles) wide. The width of the mouth of the river is usually measured from Cabo do Norte to Punto Patijoca. Generally, the outlet of the Para River is included. It is 60 km (37 mi) wide, and forms the estuary of the Tocantins . The estuary also includes the island of Marajó, which lies in the mouth of the Amazon. This means that the Amazon is wider at its mouth than the entire length of the Thames in England.

Along the coastline, near Cabo do Norte, there are many islands partially covered with water. There are also sandbanks. The tides of the Atlantic generate a wave that reaches into the Amazon river. This wave goes along the coast for about 160 kilometres (99 miles). Thephenomenon of this wave generated by the tides is called tidal bore. Locally it is known as pororoca. The pororoca occurs where the water is less than 7 m (23 ft) deep. It starts with a loud noise, and advances at a speed of 15–25 km/h (9–16 mph). The bore is the reason the Amazon does not have a delta. The ocean rapidly carries away the large amount of silt brought by the Amazon. This makes it impossible for a delta to grow past the shoreline. It also has a very large tide, that can reach 6 metres (20 feet). The place has become popular for river surfing.

A phenomenon that is very similar occurs at the mouth of the Orinoco.