The willows and the cattle grazing on the flood plain are as timeless and tranquil as a Constable painting, but it is the pictures beneath the water that draw my gaze. As the canoe glides between tall clumps of true bulrush, the gin-clear river reveals a secret garden – tresses of trailing waterweed, water lilies and other delicate, dazzling green aquatic plants. Between them, fish dart constantly – plump chub, red-finned perch and shoals of minnows.

I am not a great canoeist, I have not powered myself down the world’s great rivers, but as a long day navigating the winding, secret upper reaches of the River Waveney unfolds, so deepens my conviction that this is the best one I have ever paddled down.

The Waveney springs from Redgrave Fen, barely 25 metres above sea level, and meanders for 60-odd miles to Britain’s most easterly coast — reaching the sea both at Lowestoft (via a channel) and ultimately at Great Yarmouth after joining the river Yare. This long, slow waterway marks the border between Norfolk and Suffolk. Although its lower reaches create wetlands that are included in the well-charted Broads, most of this graceful river valley is absent from visitor itineraries and tourist trails.

This is quiet, unspectacular English countryside possessed of an intriguing recent past. In the 1960s, writers, artists, crafters and bohemians were attracted to the Waveney Valley by a growing countercultural community and the fact they could buy a derelict farmhouse for a few thousand pounds. One enthusiastic incomer was the nature writer Roger Deakin, who later made an illuminating radio documentary, Cigarette on the Waveney, about travelling down the river on a canoe called Cigarette.

I want to follow in Deakin’s ripples, and so with my expert canoeist friend Nick (and his beautiful canoe, Tern), I drop into the river at Shotford Bridge, near the town of Harleston. Deakin famously asserted his right to enjoy British waters that are often, bizarrely, in private ownership, but I decide Guardian readers should only be encouraged to canoe along a 14-mile stretch with agreed access, portage points (where we have to lug the canoe over land to avoid a weir or mill) and a British Canoeing route-guide online.

A woodpecker cries and a heron flaps away warily as we head downstream along the narrow river. Our eyes are soon drawn down to the marvellous scene below the water, which unfolds like the view from a fast train. I can’t help shouting with amazement at the massive fish flexing between fronds of green.

As Deakin said in his gorgeous radio broadcast: “The Waveney for me, as my local river, has always been a kind of escape route. It’s a way into another world.”

He’s spot on. Moving along at water level, we are concealed from the land beyond, and it is mostly hidden from us. At a portage point above the village of Homersfield, Nick and I sit on the bank for a quiet minute, transfixed by the minnows in the golden water, between the trailing weeds and sandy bottom. Deakin likened this disorientating view to “being in a plane, looking down at a rainforest”. Nick points out that this private other-world would’ve looked just like this 5,000 years ago; it’s rare to find such portals on land, but water provides them because it can’t be ploughed or built on.

It is an exciting, meandering morning. We have to shimmy into horizontal positions to slip under a fallen willow. At times, the river narrows to a slit between 8ft-high clumps of bulrush. Abruptly, the water widens into magical and unexpectedly deep lagoons, perfect for a wild swim in warm weather.

The only people we encounter on the river all day are two other canoeing parties and a fisherman wrestling a gigantic chub. Beside the ornate miniature industrial bridge (an early example of concrete) at Homersfield, we meet children messing about in the shallows. Their parents helpfully confirm that yes, the Black Swan does serve food.

We tie up, enjoy a fine lunch and a real ale in the beer garden and continue downstream. A kestrel hovers over the valley meadows. Around us bounce banded demoiselles, which resemble emerald and black water butterflies.

At Earsham, we pass the spiritual home of the otter, the former headquarters of the Otter Trust, where otters were bred and reintroduced across England. By now Nick has seen a water vole and I’ve spied three kingfishers. It’s so bountiful I’m surprised that we don’t stumble upon an otter.

I keep expecting the river to widen out but instead it divides, and between Earsham and Bungay is the hardest section, with reeds at times conquering the river. We force through and wiggle round fallen trees. At one point we have to get out and push. Finally, as we draw beside Bungay’s castle and old houses, built into the river cliff, the waters widen. The last stretch, a couple of miles around “the Bungay loop” is broad, easy paddling as the river horseshoes across the valley and returns to the east end of this pretty little market town, which is well worth exploring.

We finish, tired and elated, at Bungay staithe, home of the Waveney Valley canoe club. We feel like visitors from another planet because, for a day, we have been inhabiting a completely different universe.

How to canoe the Waveney
The 14-mile route from Shotsford Bridge to Bungay Staithe is a long day’s canoeing; alternatively, take two days with an overnight stay in Homersfield. The best way to do it is in Canadian canoe or an inflatable kayak. For canoeing the Bungay loop (and on to Geldeston Lock), Canadian canoes for up to four people can be hired at Outney Meadow caravan park in Bungay (£50 a day, £35 half day, until end of October, reopens 1 April). Captain Cook Canoes at Wortwell Mill (closes end of September) rents kayaks (£40) and Canadian canoes (£45) for the scenic three-hour paddle to Mendham and back. Canoeing downstream is recommended – the overgrown Bungay-Earsham section in particular is difficult upstream. Canoeists can continue further downriver from Bungay to Geldeston Lock, where The Locks Inn is another nice riverside pub. The stretch from Geldeston to Beccles is open to motor boats but still canoeable.

Where to stay
Camping available at The Black Swan in Homersfield from £15 a night. Cabin/wagon/shepherd’s hut at Roger Deakin’s former farmhouse in Mellis, via Airbnb, from £100 a night (two nights minimum). Temple Bar House studio in Bungay, via Airbnb, from £85 a night (two nights minimum).

• This article was amended on 24 September 2020 to clarify details for how the Waveney river reaches the sea.