MSC Barcelona container carrier ship leaving Guanabara Bay with Sugar Loaf on the background.
In order to enter and leave Guanabara Bay, large ship owners must hire pilots. The currents can be strong and the shallow depth is also a challenge.
Guanabara Bay isn’t deep enough in many locations and in order to enter or exit it when piloting a large vessel, one must know where exactly to steer it.
Underwater geography is marked by remains of the last ice age. When the sea receded, the coastline was hundreds of kilometers away and all the streams/rivers flowing to the bay formed a major river on the middle of it, carrying sediments and deepening the central areas of the bay we know today.
This deeper channel, which is not at all visible from the water surface, is used as the main waterway to and from areas on the back of the Bay and was vital to the formation and now the maintenance of the industry around it.
Guanabara Bay nautical chart: http://www.gpsnauticalcharts.com/main/br_1501_1-baia-de-guanabara-nautical-chart.html
Photo taken on 15/May/2016.