It was Robert Louis Stevenson’s famous maxim that it is better to travel hopefully than to arrive. In Cambodia, he would be pleased to know, you can now do both.

The arrival is at Angkor, the sacred metropolis buried in the jungle with its hoard of a hundred temples, including the famous Angkor Wat. The hopeful way to travel there is via the River Mekong, and its Cambodian tributary, the Tonlé Sap. You can now get to Angkor on a comfortable new cruiser called the Toum Teav. It looks like being the first of a small flotilla of riverboats that will sail to Siem Reap and the temples — either from Phnom Penh, the low-key capital of Cambodia, or from Ho Chi Minh City (Saigon) in Vietnam, via the Mekong delta.

For me, this was a journey of two halves. I had hoped to travel all the way by river from Ho Chi Minh City, but my schedule did not match Toum Teav’s. Instead, I got a taste of the Mekong — whiff would be more accurate — aboard a Vietnamese cruiser, the Mien Tay.

It was an insalubrious start. As Ho Chi Minh City’s high-rise centre recedes, the shanties start and the river deteriorates. The water is foul, black and smelly; the banks, where you can see them through the tumult of houseboats, are fetid with waste. We were sailing on a sewer through a slum, and the general grimness was only alleviated by a passing funeral.

Through the squalor it came: a sampan hearse bearing a coffin shrouded in startling yellow silk and shaded by a maroon velvet canopy. Another boat followed with the family mourners, and then a ferry crowded with people in immaculately laundered cotton. The cortege passed as quickly as it had appeared; so too did the slum. The Mekong, ever industrial, was no longer urban. Clumps of water hyacinth drifted on the stream; condescending palms stooped from the banks; rickety tin shacks tiptoed into the water on spindly stilts, each with a boat parked in the mud beside it.

Vietnam seethes with movement; nobody just sits. If the people are not buying, they are selling; if not making, mending; and if they are not planting, they are building — highways, bridges, factories, homes. The water is charged with perpetual motion — there are brand-new freighters built of steel, with spotless family quarters in the stern and the lucky eye painted on their bow; there are barges pulled and prodded by tugs; and traditional plank cargo vessels with high prows and slab sides.

There are slender sampans, with a man at the tiller and a woman in a coolie hat squatting, uncommunicative, in the bow. These carry everything — pigs, coconuts, coffins. We were the only people on the river for fun, apart from the small boys swimming in the gravy-brown water. “They do everything in the river,” said Son, my interpreter, unambiguously. “Except drink it.”

THE MIEN TAY is a cross between an ark and an outhouse. She has the big-bellied hull of a Mekong cargo boat, with a tool shed bolted on top. At first sight, it seems promising. You board in the bow, which curls up like a wood-shaving, and enter an airy saloon whisked by ceiling fans. The deck is scored with saw marks, and every surface is thick with varnish, like the crust of crème brûlée. So far, so rustic. Moving aft, there are three washrooms, and then, through the galley, an attractive little veranda on a poop deck.

But then it dawns on you: the saloon is the passenger quarters. Full stop. It is where we will eat, sit and sleep — or try to — on spongy foam-rubber mattresses. There is shelf room for 16, but without a vestige of privacy, neither curtains nor compartments. As for the inviting veranda, that’s strictly for the crew. I was lucky: Son and I were the only passengers.

On the first night, we anchored a little before eight. Now what? We had finished supper (chicken soup, prawn dumplings, steamed fish — fresh and delicious, like all the meals on the Mien Tay), and wanted no more to drink. It was too dark to read, and I couldn’t face going through Son’s love life — or lack of it — again. It was going to be a long night.

There can be few rivers noisier than those lower reaches of the Mekong. All but the most substantial boats in Vietnam are powered by outboards — Chinese cultivator engines with madly spinning flywheels, which balance at the end of long, trailing propeller shafts. It is like being surrounded by lawnmowers.

Boats passed sporadically throughout the night. Either I managed to sleep through them, or I incorporated their racket into my dreams. But, at six, the mowers swarmed. As soon as we could, we moved.

A hundred or so vessels were moored in two lines off the town of Cai Be. These were sizable family boats with cooking pans and washing around their sterns; dogs and children on deck. The only clues as to why they had gathered were tall bamboo poles raised vertically, like antennae. On top of each hung vegetables or fruit — cassava, sweet potato, pumpkins, tomatoes, sugar cane and rambutans. This was Cai Be’s floating wholesale market: the boats were warehouses, not shops. Fussing between them, sniffing for bargains, were little sampans stocking up for the day’s trade.

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