A biathlon combining running and swimming is a multisport race where athletes complete both disciplines back to back, with their combined time determining the result. Depending on where you are in the world, this event goes by different names: “aquathlon” is the term used by World Triathlon (the international governing body), while “modern biathlon” is the term used in the UK, particularly in schools and youth programs run by Pentathlon GB. Either way, the concept is the same: run and swim as fast as you can, with a short transition between the two.
How It Differs From the Winter Biathlon
If you searched this expecting cross-country skiing and rifle shooting, that’s the winter biathlon, an entirely separate sport governed by the International Biathlon Union. The run-and-swim version shares only the name “biathlon,” which simply means “two contests” in Greek. The confusion is common, but the two sports have no organizational overlap.
Standard Distances
The most widely used aquathlon format for adults is a 1 km swim followed by a 5 km run. Junior and youth races use shorter distances scaled by age group, and many events take place in pools rather than open water, making them accessible to newer competitors. Evening and weekend aquathlon race series are popular with local triathlon clubs during the summer months, so these events are often a first step into multisport racing.
In the UK’s modern biathlon format run by Pentathlon GB, the race comprises a run and a swim that can be held in either order. Distances vary by age category, and there is a scheduled break between disciplines rather than a rapid transition. If two athletes finish with the same combined time, the tiebreaker goes first to the faster run time, then to the faster swim time.
Race Format and Transition
Most aquathlon races follow a run-swim-run or swim-run format. In a swim-run event, you exit the water, move through a designated transition area, change into your running shoes, and head out on the run course. The transition area is a marked zone where your gear is laid out beforehand, typically just shoes and a race belt since the equipment demands are minimal compared to a triathlon.
One thing that catches first-timers off guard is the physical sensation of switching from swimming to running. Going from a horizontal position in the water to standing upright and immediately running can feel disorienting. Blood rushes to your legs, your balance is briefly off, and your heart rate spikes. This passes within the first minute or so of running, but it’s worth practicing beforehand so it doesn’t throw you on race day.
If the swim takes place in open water and you’re wearing a wetsuit, you’ll need to strip it off in transition. The fastest approach is to unzip and peel the suit down to your waist while jogging toward your gear, then pull it off your legs once you reach your spot. Lubricant on your arms and lower legs makes removal significantly faster. For pool-based events, most athletes simply race in a one-piece or two-piece racesuit and skip the wetsuit entirely.
What to Wear and Bring
The gear list is refreshingly short. A racesuit (either one-piece or two-piece) that works for both swimming and running is the core piece of equipment. Beyond that, you need goggles, a swim cap (often provided by the race), and running shoes. No bike, no helmet, no cleats. That simplicity is a big part of the appeal for people who want to try multisport racing without a major equipment investment.
If you’re racing in open water at cooler temperatures, a wetsuit may be required or optional depending on the water temperature and race rules. For pool swims, you won’t need one. Lay everything out in the transition area before the race so you can move through it quickly: shoes open and ready, race number pinned to your racesuit or clipped to a belt.
Who Governs These Events
At the international level, World Triathlon sanctions aquathlon events, including the annual World Triathlon Aquathlon Championships (the 2025 edition is scheduled for Pontevedra, Spain). National federations affiliated with World Triathlon, such as USA Triathlon, organize domestic races and qualifying events.
In the UK, the modern biathlon sits under Pentathlon GB, which oversees the sport as part of its broader modern pentathlon development pathway. Schools biathlon competitions are particularly popular, serving as an entry point for young athletes who may eventually move into pentathlon or triathlon.
Why People Choose It Over Triathlon
The most obvious reason is no cycling. That eliminates the most expensive and logistically complex part of triathlon. You don’t need a road bike, clip-in pedals, or a bike rack on your car. Race-day setup takes minutes instead of an hour. For swimmers who also run, or runners who also swim, the aquathlon lets you race both strengths without a discipline you may not enjoy or can’t afford to equip for.
It’s also a natural starting point for kids. Many schools and youth programs use the swim-run biathlon format because pools and running tracks are readily available, the risk profile is lower than open-road cycling, and the events can be completed in a short time window. Athletes as young as eight regularly compete in age-appropriate distances.