You cant claim to really know a city until you’ve had a conversation about its sewage with an aquatic ecologist from the local water board. I’d not given much thought to what goes on beneath Amsterdam before I met Laura Moria in a coffee shop near the Anne Frank House. Laura spends her life scrutinising the canals, scooping and testing and doing whatever aquatic ecologists do to keep tabs on microscopic nasties. Until recently, it was a job that required a strong stomach and a nose peg. “The canals used to stink,” she tells me. “They contained untreated sewage, and if you fell in you’d be rushed off to hospital fora tetanus jab.”

But the past decade has witnessed a concerted push to clean things up. Thousands of houseboats have finally been linked to the sewer system, and a special vessel patrols the channels with a net to skim off floating rubbish. There’s even a boat dedicated to hooking out the 12,000-odd bikes that are chucked in the water annually. The results have been dramatic — so dramatic, in fact, that a round 2,000 people jump into the canals of their own accord during the Amsterdam City Swim each September. “Even our Queen has taken a dip,” Laura says. The flora and fauna are also flourishing in t he purer water. Yellow water lilies flower in summer, while water fleas zip about eating algae and are in turn gobbled up by fish t hat had previously given t he canals a wide berth. Pike, eels and carp have all returned, along with the herons that stalk them, and coots that dabble among the reeds.

There are bullhead fish, sponges and mussels, and — Laura’s favourite — a snail wit ha head like a smurf. It’s a smorgasbord of life. “Our tap water is filtered through the sand dunes — you must try it,” Laura urges, as she pays for her cappuccino. “Oh, and look out for canal lobster on the menu,” she adds cryptically over her shoulder before the door closes and she’s gone. Canal lobster?! While there’s a limit to how exciting I can find the prospect of a good glass of tap water, t he mysterious canal lobster sounds like something altogether more enticing. I vow to track one down. But first — a boat tour.

ON THE WATER

If there are newfound riches hidden below the surface, those above have been plain to see for centuries. Amsterdam is a city built on water, both literally and metaphorically, the horseshoe of canals at its heart constructed during a period when the Dutch ruled the waves and this was the world’s greatest port. The stylish way to explore the trappings of that 17th-century Golden Age is aboard a saloon boat with teak flooring so polished you can skid from bow to stern. The Tourist is moored outside the equally dapper Hotel Pulitzer Amsterdam, which fills a row of converted canal houses. My skipper has a smart epaulette on each white-shirted shoulder and a sailor’s cap sitting level on his head. Even the letters of his name are arranged tidily. “I’m Onno,” he says. “Although people who know me tend to cry ‘Oh, no!”’

Onno’s justly proud of his craft, a 43ft beauty built in 1907 to transfer guests to their accommodation. Today, transformed from diesel to eco-friendly electric, it carries a maximum of 12 passengers. “A more personal sightseeing experience — this is the cork we’re floating on!” says Onno, nosing us through a low-slung bridge separating the grandly titled Emperor’s Canal from the more blue-collar Brewers’ Canal. Reminders of the city’s ocean-going history are everywhere. We pass the monumental sweep of Amsterdam Central station, a wind dial on its tower to assist sailors, and the Basilica of St Nicholas, dedicated to the patron saint of seafarers.

The waterway widens and we round the green hull of Science Center NEMO, designed by Renzo Piano to look like the prow of a hulking tanker, and then a full-size replica of the Amsterdam — a Dutch East India Company cargo ship that was stranded off Hastings in 1749 — a sign we’ve reached the jetty of the Maritime Museum. The Dutch East India Company is synonymous with the Golden Age. Founded in 1602, it was the first-ever multinational, making gargantuan profits importing spices from the Far East. Amsterdam grew into the ‘warehouse of the world’, handling everything from timber and wine to subtropical fruits and porcelain. The 17th century was a very good time to be a Dutch merchant, and their lavish mansions are strung along the most exclusive stretch of canal.

Onno spins his brass wheel to take us there, making a lazy arc into the broad-beamed Oudeschans — a former ship-building canal where vessels like the Amsterdam would have started life — past a tilting lock-keeper’s house that’s now a pub. Past the Rembrandt House Museum, the site of the artist’s home for 20 years, where he painted the masterpieces that make him a totem of the Golden Age. Then a left and a right and we reach our destination: Herengracht (‘Gentlemen’s Canal’).

This was for the wealthy set. Lofty merchants’ houses with gables like elaborate headdresses face each other across the water, as if waiting for the orchestra to kick-start a masquerade dance. And the so-called Golden Bend boasts the grandest residences of all, their double width plots available only to those with pockets as deep as ditches. “The fronts are nothing,” Onno comments as we drift past. “You should see inside!”

BEHIND THE FACADES

Museum Van Loon, here at Emperor’s Canal 672, offers the chance to do just that. “The van Loon family made its money in herring,” Tonko Grever, the museum’s director, tells me. I glance around the cavernous entrance hall with a new respect for rollmops. This was a powerful dynasty: Willem van Loon became mayor of Amsterdam and his son ruled over the East India Company for 30 years. We walk through reception room after reception room, up a sweeping staircase to bedroom after bedroom, out into gardens with manicured hedges, a golden sundial and a brick-floored coach house flanked by classical statues. There are cherry-wood chests, four-poster beds, stuffed peacocks on mantelpieces. And, everywhere, vast portraits of van Loons in ermine or pearls, for Amsterdam’s merchants loved commissioning paintings of themselves.

“Rembrandt’s paintings weren’t for museums,” Tonko reminds me. “They were hung in private houses like this.” But for all the bounty earned on the high seas — all the piles of pearls and peacocks — Amsterdam’s elite has found that water can be foe as well as friend. Canal houses stand on wooden foundation piles driven deep into the mud, and when the water drops the piles rot. This is why some houses are oddly lopsided, leaning against neighbours like walking wounded, their foundations subsiding beneath them. Nowhere is wonkier than the restaurant De Silveren Spiegel (‘The Silver Spoon’), where I eat that night. Christopher, a waiter — “and storyteller!” — takes me on a tour.

The restaurant occupies a pair of houses built in 1614 by Laurens Spiegel, another leading merchant and city mayor (although Laurens made his name in the glamorous world of soap-boiling rather than herring). With skew-whiff windows below its stepped gables and floors that sag like washing lines, The Silver Spoon is the crooked house of fairytales — so it’s perhaps fitting that it requires a rainbow’s pot of gold to maintain; the foundations have been reinforced once already, and further work is required next year. What doesn’t need fixing is the cooking — dishes of Dutch shrimp, beef loin and blood-orange mousse are as good as anything you’ll eat in Amsterdam. But what about canal lobster? “Erm, no” says Christopher, carefully, as if humouring a madman. “If that’s a real thing, the Kitchen of the Unwanted Animal might sell it. They’ll be at Rolling Kitchens.”