Congo River, the depth of the river varies a lot depending the location. The Congo River is the deepest river in the world with measured depths in excess of 220 m. But some places are very shallow. Places where boats might get stuck on sandbanks for weeks. That's why every boat has a 'sondeur'. French word for sounder (are in German Echolot) who measures the depth of the river with a long stick. He shouts the measurements when he touches the riverbed.