You'd think sitting at the harbour's edge on a ridiculously sunny day would be relaxing, but it's not. Instead, it's exciting. Majestic ferries power by, punctuated by deep-throated jetboats loaded with adrenalin junkies. There's a big, moored cruise ship, and the Opera House looks as if it's about to move gently out to sea. Even without the light shows of Vivid kicking in from May 27 to June 18, Sydney is just so "activated", so full of energy and optimism right now.

And here, right in the middle of it, is Whalebridge, a new French bistro opened on the site of the old Sydney Cove Oyster Bar by Fraser Short's Sydney Collective. It's so sunny, they're handing out smart white Panama hats to wear. It's so sunny, I have to order Sydney rock oysters from Merimbula ($5.50 each) on a bed of crushed ice, drowned in briny juices, and a glass of the ripe, herbaceous Daniel Chotard sancerre ($25).

The menu, from chef Will Elliott (Hubert, Cumulus Inc., St John), goes for seafood through a French bistro filter, with nostalgia on the side. Big share platters of fruits de mer, bouillabaisse, bowls of mussels and even ye olde lobster thermidor compete with twice-baked comte souffle, rillettes de porc, rotisserie chicken and steak frites.

There is a list of tins, too, of marinated red peppers, anchovies, or fat, oily sardines with tiny Nicoise olives ($26) that come with crisp sheets of pane carasau. Cute idea – everyone needs a tinny by the water.

But that's on a sunny day, right? Whalebridge is completely al fresco, its 260 seats under umbrellas with two small and charming Federation brick buildings reserved for kitchen and service bar.

What happens at night, in the dark? That's when the restaurant flips to setting lamps on tables, handing out knee rugs and firing up gas heaters. If it rains (because it has been known to), they make back-up reservations at the group's other city venues, The Morrison and Republic Dining.

But as manager Ludovic Lemaitre says, "When it's beautiful, it's beautiful." So let's stay as sunny as the staff, with their jaunty blue-and-yellow scarves and French accents, as they ferry sweet little yellow-rimmed plates to tables.

House-baked fougasse, that very Provencal olive oil bread, comes with a play on French onion dip ($12), a gorgeous, whippy cream of confit onion, celery salt, creme fraiche and fried shallots.

The crowd – locals, country folk, overseas tourists – is also digging the share dishes. Moules marinieres ($55) sees a kilogram of the ever-reliable Kinkawooka mussels in a silky wine-based cream that announces very loudly the chef knows what a classic sauce is. Frites are salty, thin and skin-on.

Lobster thermidor is market price (today's, not the 1970's sadly), and an 800-gram Eastern rock comes in at $170 to feed two, topped with a mountain of tiny crisp matchstick potatoes. It's luxe without being overly cheesy, a close cousin to the classic listed in Larousse Gastronomique – and it sure as hell says you're on holidays.

So does a modern take on courgettes farcie ($36), the sliced zucchini twirled around a pleasantly oily mix of eggplant, tomato and tapenade.

Desserts are prepared in the group's central production kitchen, and a nicely tangy tarte au citron ($14) is otherwise pedestrian, with a firm skin on top and over-baked pastry below.

The drinks list, on the other hand, is as broad as the Harbour Bridge, with everything from Kronenbourg lager to an eye-popping reserve list with a Domaine Jean Tardy et Fils Echezeaux Grand Cru 2017 for $985.

There are obvious drawbacks to a restaurant not having a roof, or even walls, but there is also something magical about it. Risk (theirs, and ours) equals reward.

So three cheers to the ambition and optimism that this slightly crazy French bistro brings to Circular Quay. They have gifted us another place to play by the waterside, come rain or shine.

The low-down

Vibe Living the dream, dining on the world's most beautiful harbour

Go-to dish Moules marinieres frites, $55

Drinks Whalebridge martini, rhubarb rosé spritz and a seaside-smart French-led wine list

Terry Durack is chief restaurant critic for The Sydney Morning Herald and senior reviewer for the Good Food Guide.