Through my mosquito net I watched dawn break over the Okavango flood waters. I had been awakened by the sound of hippos harrumphing in the river. Now, as the coucals cried from the reed beds, I looked over our stern to a horizon so flat and so wide I could sense the curve of the earth as it rolled through space to meet the rising sun.

No wonder Prince Harry loves this wild African river. And no wonder he chose to explore it — twice; most recently a couple of weeks ago for his 25th birthday — aboard the Kubu Queen, a double-decker houseboat based at the waterside village of Shakawe, in northern Botswana.

From here, at a stately seven knots, she embarks on leisurely cruises up and down the Panhandle, the northern reaches of the Okavango River, near the Namibian border. In all but name she is a floating safari lodge, 40ft long, moving every day from one idyllic mooring to the next, with an outboard-powered skiff in tow for birding and fishing expeditions.

Built 25 years ago, she has enjoyed a chequered career. She started life as a ferry, but sank in the late 1990s. Five years ago, Greg Thompson, her present owner, bought her for a song and lovingly restored her, complete with shower, flush toilet and an array of brass signs, one of which reads: “Ship’s bar — open from 09.00 to 08.59.”

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In truth, she is a slightly raddled old matriarch, so don’t expect the red-carpet experience when you step aboard. Her paintwork is faded, her varnish blistered by too much time in the African sun. What she offers for six lucky passengers is simple comfort, sumptuous meals and bags of character. And what’s good enough for Harry is good enough for me.

As we cast off, a late-afternoon storm trails curtains of rain across next-door Namibia, but where we are the sun shines warmly. We go with the flow, cold beers in hand, and drift downstream on the swirling current, over amber depths so crystal clear I can see the bottom 12ft below. We spot a cluster of bee-eaters balancing on a swaying reed stem, and a fish eagle in a dead treetop. As we chug past, it flings back its head and utters its wild, yelping cry — the authentic voice of the Okavango.

What an extraordinary river this is. It rises in the mountains of Angola less than 200 miles from the Atlantic. But then, perversely, it strikes out in the opposite direction, heading for the Indian Ocean on the other side of Africa. For a thousand miles it flows strongly, until, in the endless flatness of northern Botswana, its waters falter. In vain they fan out through the papyrus swamps, struggling to reach the Kalahari beyond, only to sink into the desert sands or evaporate in the scorching sun.

But before it dies, this river of no return spreads out to create one of the most extraordinary places on earth. The Okavango Delta is Africa’s biggest oasis: 10,000 square miles of reed beds, islands, lagoons and flood plains braided by a maze of channels. Bits of the Panhandle remind me of the Norfolk Broads, all thatched wooden houses and neat waterside lawns, but there are parrots in the treetops and hippos instead of motor cruisers.

One morning, Thompson takes us ashore for a stroll in the forest. We cross riverside glades lit by swarms of glittering dragonflies and find the two-toed tracks of a sitatunga, a shy, swamp-dwelling antelope that moves through the papyrus by using its cloven hooves like pincers to clasp the reed stems. If it feels under threat, says Thompson, it will hide underwater with only its nose above the surface.

In his time, Thompson has been a professional hunter and a safari guide, but his greatest passion is angling. That’s why he lives here, and if you’re a fisherman, there is no better time to be here than during the barbel run. This is one of nature’s great events and it happens every year, from August to October, when thousands of barbel pour down the river, hunting the smaller fry that breed in the shallows. Birds and animals join the feast: otters, fish eagles, herons and pelicans. Flocks of egrets smother the reeds like falling snow.

“Sometimes there are so many fish that the water seems to be boiling,” says Thompson. “And among them are the tiger fish — voracious predators that have made this one of the world’s top sport-fishing hot spots.”

Every day towards sundown, when the painted reed frogs begin to call like ice cubes clinking in a glass, we moor up for the night under the jackalberry trees. A campfire is soon glowing on the river bank. Now’s the time to listen out for the fishing owl, a local rarity that attracts birders from all over the world.

By day it hides in the darkest treetops, seeking refuge from the fish eagles that are its sworn enemy. But at night it emerges to feed on fish, frogs, even small crocodiles, and it is then you may hear the gruff voices of the adults or the eerie cries of the young — “Like a lost soul falling into a bottomless pit,” says Thompson. Next morning, we skim down a quiet backwater in the skiff, going ever deeper into the secret world of the papyrus.

Looking like painted images from a pharaoh’s tomb, its tasselled tops close in around us. There are 350 bird species here, including pygmy geese, goliath herons and giant kingfishers the size of chickens. We surprise a family of spotted-necked otters playing follow-my-leader, then suddenly emerge to see the open flood plains spread out before us.

It’s an extraordinary spectacle. Where cattle normally graze, wild duck are swimming and trees stand up to their ankles in water. We putter for miles across this strange, drowned land, forging a path through fields of water lilies. It is so inexpressibly beautiful that, when at last the sun goes down, we can hardly bear to turn for home.

Travel details

Brian Jackman travelled as a guest of Cazenove & Loyd (020 7384 2332, cazloyd.com ); it can tailor-make a one-week safari in Botswana from £2,960pp, including three nights on the Kubu Queen, full-board (kubuqueen.com ), and three at a luxury tented camp, all-inclusive, with game drives, the final night, B&B, at The Grace in Rosebank Hotel in Johannesburg, flights from Heathrow with Virgin Atlantic (virgin-atlantic.com ), connecting flights from Johannesburg to Maun in Botswana, and onward light-aircraft flights and transfers. Or try Aardvark Safaris (01980 849160, aardvarksafaris.com ) or Steppes Travel (01285 650011, steppestravel.co.uk ).

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