And then there are the hippos.

We set off mid-morning – three couples, a guide, a cook and four double canoes – from the bank of the fat and surprisingly fast Zambezi river. As we packed our boats (fibreglass, tents in the middle), our guide dispensed laconic instructions and factoids (a hippo can stay underwater up to six minutes at a time, reappearing pretty much anywhere).

Now he donned a Rambo-style sweatband, raised a fist and whooped us onward. (Oh great.)

What did I know of Africa? Picture books and bedtime stories. When I was a child, one of my favourite was The Elephant's Child by Rudyard Kipling. The young elephant who sets out alone to find the great grey-green, greasy Limpopo river and discover the answer to the question no one will answer: What does the crocodile have for dinner?

What indeed.

Bobbing around us as we slide into the current are the blunt snouts of very many hippopotami. Some have calves.

We know already that this makes them more than usually nervy – a fact that our guide (let's just call him Rambo) repeats with relish; along with helpful tidbits on the crocodiles that animate and slip soundlessly into the water as we pass. ("There's a big one.") We have a pretty good idea what the crocodiles would like for dinner.

After six months travelling here, my partner and I know too that crocs are not even our greatest threat. Mosquitoes and humans aside, that distinction goes to the hippo (which while mainly vegetarian is fiercely territorial). Elephants. Black mamba. Lions. We have read plenty of articles about animal encounters with stupid tourists. Stupid dead tourists.

We know all sorts of things:

• Keep away from the river's edge (unless you like crocodiles);
• The person in the back sets the course; the one in the front looks out for trouble;
• Never get between a hippo and deep water.

But none of it seems to help.

We are falling apart. While the other couples seem instantly to master the basics of navigation, my partner and I are unable to travel in a straight line. I steer in one direction, he pulls in the other. They glide; we zigzag. We have no idea where the deep water is. Or even that we are already in it.

I still remember the queasy excitement of the elephant's child's quest. The unanswered question. The kolokolo bird with its mournful cry: "Go to the banks of the great grey-green, greasy Limpopo River, all set about with fever-trees, and find out." Which he did (arriving with a snub-nose and leaving with a trunk). We too have brought our own questions. Not that we discuss them. Like the hippos they lie semi-submerged, and we do our best to avoid them.

Halfway through the third morning, it becomes clear the hippos are winning. Everywhere we turn the cows are sinking or bursting up around us like liquid boulders. Rambo makes a decision. He leads us off the main river and onto a shallow tributary. Relief. Deep water behind us. And then we meet daddy hippo. "This looks like trouble," says Rambo.

Over the next 20 minutes or so, as we attempt to sidle past in our canoes, the bull charges us repeatedly. We thwack our paddles on the water's surface and he retreats a little; we resume, he charges. And through all this my partner and I continue our tug of war. At one point we actually pirouette. Its teeth are enormous. Thwack. Thwack.

By the time Rambo orders us out of our canoes to drag them through the crocodile-infested waters and past three tonnes of snorting muscle and mouth, I am almost beyond caring. I am going to end up in one of those articles about stupid dead tourists. And for what? What have I learnt?

That evening – our last on the river and one of our last in Africa – we set up camp on a sandbank and watch the river turn aqua and apricot. My partner, who I love but cannot navigate, sits companionably beside me. Across the way in Zambia the mountains recede in shades of slate. An elephant – folds of prehistoric grey – flaps its ears absently and dips its trunk to harvest great sheaths of silver grass. The clouds are golden. They emanate. It is over.