What's the biggest obstacle to traveling by boat on the congo river?

This would be shallow rivers. They're the biggest obstacles by boat on the Congo River.
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C. shallow areas due to drought

Explanation:

The congo river is the second largest river of Africa and has a length of about 4,700km and has a basin area of about 4,014,500 km square. The congo river is a major  transport route carries 86 million tonnes of the suspended sediments towards the Atlantic ocean and about 6% in the bed load. But in the dry season the river is unable to carry and deposit the load and thus forms a bigger obstacle as major rapids hence not navigable.

Csaudi arabia and wish u us: )