Only around 1,249 Yangtze finless porpoises are estimated to remain, and that number is engraved on this watch. The Oris Yangtze Jiangtun Limited Edition is an Aquis Date made to support the Changjiang Conservation Foundation in its work to save the critically endangered species.

The details tell the story. The green mother-of-pearl dial has a pattern inspired by the sound waves of the porpoise’s ultrasonic clicks, so it glows and ripples in the light like the river surface. The edition is limited to 1,249 pieces, one for each porpoise in that estimate, and each is numbered on the engraved caseback. A tungsten minutes-scale ring on the bezel adds a dense, dark gleam that sets it apart from standard Aquis models.

As a dive watch, it is the full Aquis package: a 43.5mm steel case rated to 300 meters, a screw-in crown, integrated lugs and a tapered steel bracelet with a folding clasp and extension. The Oris 733-1 automatic offers 41 hours of power reserve.

Aquis Date Yangtze Jiangtun Limited Edition, Ref. 01 733 7789 4197

• Reference: 01 733 7789 4197-Set, limited to 1,249 pieces
• Case: 43.5mm multi-piece stainless steel, about 13.1mm thick, 23mm lug width
• Bezel: unidirectional with tungsten minutes-scale ring
• Dial: green mother-of-pearl with sound-wave motif, Super-LumiNova
• Movement: Oris 733-1 automatic (Sellita SW 200-1 base), 28,800 vph
• Power reserve: 41 hours
• Crystal and back: domed sapphire; screwed steel caseback with engraving
• Water resistance: 30 bar (300 meters)
• Bracelet: stainless steel with folding clasp and extension

A capable diver that keeps a vulnerable river species in mind.