An Olympic-length swimming pool, therapy baths, and rooftop running track is floating on the Seine inside a sleek, steel-structured barge named Annette K.. Designed for public use year round, it’s a bold return to river life, made possible by the quiet strength of molybdenum-containing stainless steel.
By Martina Helzel, IMOA
In the heart of Paris, something remarkable has taken shape on the water. Launched through “Reinventing the Seine”, a city initiative to bring new life to the river, Annette K. is part of a broader ambition. The goal is to reconnect Parisians with the Seine, not only visually but also physically as a place to swim, move, and gather. In design, spirit, and material performance, Annette K. marks a new chapter in Paris’ relationship with the water that shaped it.
A legacy reimagined
Annette K. takes its name from Australian swimming icon Annette Kellermann, a pioneer of women’s sports and wellness. As a child, Kellermann suffered from rickets and began swimming to strengthen her legs, a remedy that transformed her life and launched her athletic career. She became a record-breaking swimmer, silent film star, and advocate for physical fitness and health. Her legacy makes her a fitting symbol for a structure that unites competitive sports, aquatic therapy, and public wellbeing.
The barge stretches 110 meters long and 15 meters wide – a compact footprint housing a 50-meter Olympic-length pool, warm therapy pools, fitness and wellness areas, spa and physio spaces, a café, and even a rooftop track. Designed by Seine Design, this multi-purpose facility supports over 2,200 users daily and stands out for its seamless integration of architecture, engineering, sustainability, and inclusive accessibility throughout.
Inside, the main promenade flows beneath the pool hull, lit by natural light and lined with wood, glass, and steel that recall the interior of a ship. Water and its rippling reflections are visible from nearly every angle. The entire vessel feels open to the elements, whether in the summer sun or on a crisp winter day.
Stainless strength and smart space
The center piece of Annette K. is a fully structural pool made from Type 316L stainless steel, an alloy containing about 2% molybdenum. This composition provides exceptional resistance to pitting and crevice corrosion in chloride-rich environments, like chlorinated pool water. The alloy was selected not only for its durability, but because it allowed for a thin, efficient structure that maximized usable space inside the floating building.
Thin steel walls mean more room for people and amenities, like lockers, therapy rooms or technical systems, without expanding the barge’s footprint. The pool shell and supporting framework double as both a water container and an architectural skeleton, eliminating the need for suspended ceilings or raised floors.
Unlike concrete, which requires thick walls, tiles, or protective coatings, Type 316L stainless steel elements can be prefabricated and then welded together on site to form the pool shell. The remarkably thin 3 mm embossed floor and 4 mm smooth wall panels create a lightweight, watertight structure. The pool won’t leak, crack, or degrade. Its non-porous surface is easy to clean and naturally resists the buildup of algae and bacteria.
Services run through the exposed ducts and steel framework with the clarity of a shipbuilder’s plan. The spider-like structural legs support walls and panels while guiding an organized network of utilities through the building, including the pool’s inflow and outflow piping, which are also made of Type 316L stainless steel to ensure long-term corrosion resistance.
Built for the long haul
From design to daily use, the material choice defines the experience. Type 316L stainless steel, suitable for life at the water’s edge, supports not just structure, but sustainability. It enables a clean, modern shell that is resistant to wear, effortless to maintain, and fully recyclable at the end of its service life. Light yet lasting, hygienic yet robust, it reflects the values of a public facility designed to serve unobtrusively, confidently, and well into the future. Annette K. is more than a pool – it is a thoughtful response to its setting. A structure shaped by water and purpose, it speaks to Paris’ evolving relationship with the Seine. A living space dedicated to the wellbeing of body and mind, it brings people back to the river in a way that is both practical and poetic.
About IMOA
Reproduced with the kind permission of the International Molybdenum Association (IMOA). IMOA is a non-profit trade association representing the majority of the molybdenum industry worldwide. For information visit www.imoa.info
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