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 . the phenomenon of this wave generated by the tides is called a tidal bore. locally it is known as "pororoca". the pororoca occurs where the water is less than deep. it starts with a loud noise, and advances at a speed of . 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 . the place has become popular for river surfing.