The course of the Niger River confused geographers and explorers for centuries: it takes a circuitous route from the hills in Guinea, not far from the Atlantic, northwards and eastwards before curving back down to the south and entering the Gulf of Guinea in modern-day Nigeria.
There’s a great series of old maps of Africa on this page, showing where people thought the Niger went: at first it was confused with the Gambia or Senegal rivers, flowing westwards - sometimes all the way from the Nile. Later it was shown as heading east, and either disappearing into a lake or going all the way to the Nile. Not until the beginning of the 19th century did anyone figure out where it actually went.
My question is, how did people miss the massive river delta? It seems virtually absent from most of those maps, even though that area must have been fairly well travelled: the port of Calabar was doing international trade from the 16th century, and according to Wikipedia British slave ships were going to and fro as early as 1815. Why did nobody put two and two together and figure out that this huge estuary might have something to do with the mysterious big river to the north? Or even mark it on maps?
From looking at those early maps it seems they thought it was a bunch of smaller rivers, like those along the rest of that coast.
The westernmost part of the delta, as far as I can tell from google maps, is Farcados:
it’s plausibly the rivery narrow triangle drawn down from the mountains and mistakenly? not colored blue on the first map
the 1644 map has R. Forcas, possibly the same, and a slew of other river names all along the delta coast
and you can see that as River Forcades on the 1710 map, which doesn’t bother with all those other “tiny rivers” along the delta
So the answer is, they didn’t realize it was a giant estuary, because most of the people in the area weren’t in the business of map making, and the ones who were weren’t in the business of modern day detailed surveying.
An accurate map was often a trade secret. Rivers are notoriously difficult to travel due to navigational hazards. Those who know a good route are not inclined to share it with their competitors.
Mostly because the rivers that reach the coast there are all rather small, and the coast doesn’t differ all that much from the adjacent areas. There is no “huge estuary.” And the old maps don’t “miss” the rivers there. They mostly do show a series of small rivers in the area. The failure was to realize the rivers were all connected higher up. But the rivers disperse into a maze of small channels through mangroves and swamp, and there is no clear main course. It’s also likely that hostile local powers resisted Europeans going any distance inland.
But as noted the main reason, even if it were realized some large river reached the ocean there, there was no reason to connect it to the Saharan part of the river. It was more plausible that the known Niger in the Sahara connected with the Nile or the Senegal. (In the latter case, its direction of flow would have to be the reverse of the actual one, but I think Europeans just knew there was large river at Timbuktu without knowing its direction.)
Another factor is that the Niger doesn’t have a huge discharge compared to other rivers like the Amazon, Congo, Ganges, or Mississippi. It’s 52nd by discharge among major rivers. Since the discharge is dispersed among the mouths, there’s not a great outflow at any single one.
Note also that the port of Calabar is on the largest estuary in that area, but that estuary is not part of the Niger Delta. It’s the estuary of the Cross River, a much smaller and shorter river that runs north and east.
(As an aside, I’ve actually been to delightful Calabar. I stayed in the Hotel Metropolitan, possibly the worst large hotel I’ve ever stayed at. When I was there in 1993, they kept the bathtubs in the rooms filled with water so you could use it to flush the toilet, because the electricity went out so often they couldn’t pump water to the upper floors.)
