We're trying to get across a river for today's Geo Quiz.

The harbour at Calabar, Nigeria

There's a river that flows near the border between Nigeria and Cameroon. In Nigeria, the river creates a boundary between two regions of tropical rain forest.

It's so wide that there are only a few bridges. Cars and trucks can get cross a half-mile-long bridge on the road between Aba and Calabar.

If you have to negotiate a ferry ride -- it might help if you spoke either Ejagham or Efik. Those are 2 of the region's languages.

The river flows through Nigeria's south-eastern-most state.

The state takes its name from the river. So does a rare species of gorilla.

Rare gorilla

We'll hear more about these creatures... when we reveal the answer to the quiz... and the answer to this riddle: how does a gorilla cross a river?