I'm running Tomb of Annihilation as a Pathfinder 2e adventure, and as usual there have been some surprises when comparing what a book says and what happens in a game. I regretted starting my players in Port Nyanzaru because, as hex crawls go, Tomb of Annihilation is not exactly the best. It's about as useful as a map generated by dice, except I had to pay $100 for Tomb. The sites the book does provide are often either severely under-developed compared to, for instance, the wilderness section of Rappan Athuk, and the illustrated maps in the book are baffling. A full map of a Merchant Prince's home is provided, but it's too small to photocopy and besides that there's no reason for a map of that to be provided. But by far the worst thing about the map of Chult are its rivers, which are apparently just 20 ft wide.
According to the map of Ataaz Muhahah, the Olung river is 20 feet at its widest point. At least, that's what's shown in the section of the river in the official map, but for a river to bottleneck down to just 20 feet, it couldn't be too much larger upstream. I guess the river could be peculiarly deep, after all this is a fantasy world so maybe this is how rivers work. However, it's also a game with specific mechanics and my players wanted to know how wide the river was for fear of zombies wading out from the shore toward their boat. A river that's 20 feet wide offers almost no protection from anything on the shore that might want to grab at them, so the question wasn't academic but strategic.
It's puzzling, because it seems like the inset picture, of the bridge dwarfing a dinosaur grazing in the valley below, is meant to emphasize the absence of water. The book says nothing about the Olung having mostly dried up. In fact, it somewhat suggests the opposite by including boat travel as a viable option for traveling through Chult. I'm guessing that the Olung was meant to have dried up when the art order was created, but later that detail got cut from the book.
On the map, you can clearly see the borders of the two cliffs that the bridge is meant to connect. It's roughly 120 feet across. The map shows just 20 feet, at its widest point, of that 120 feet being occupied by water, and the rest is filled in with tree tops and grass.
In the end, we agreed that the map is wrong. Instead of a major rain forest river that's 20 feet wide, we decided that there was water in the entire 120 foot span of the canyon. That's still arguably a pretty small river, but then again the book doesn't make any claims about the size or grandeur of Chult or its rivers. And anyway, it's a nice managable size for game mechanics that often work in increments of 30 feet.
We're still mid-campaign but I'm determined to run Tomb of Annihilation again for a separate group, this time starting them in Omu itself. I don't know how it would go, but the idea intrigues me. Either that, or else just drop the death plague altogether. As a hook, the death plague has so far failed miserably. I even tied it to my player's characters from the previous campaign, but the players still forget what the main quest is. Artus Cimber and the Frost Giants and all the other distractions aren't helping.
However, had I skipped the hex I'd have missed out on sneaking Tomb of Horrors into the campaign. The Tomb of Annihilation tells you to hand your players a map of Chult at the start of the game (Syndra Silvane gives them one) and then fails to provide interesting stories for many of the locations clearly marked on the map. So for one of the dud locations, I added the Tomb of Horrors as a dungeon crawl. I've run Tomb of Horrors before and find that most people overestimate its deadliness against modern RPG character builds, so I'm pretty comfortable sending low level characters into it. And of course, Tomb of Horrors is the dungeon and lore that Tomb of Annihilation reinvents (or reiterates, or reimplements) so it's a nice way to sneak in an homage to the original.