Swim Run should really be called Swim Run Swim Run, because you dont just do one sport and the other. You keep switching between them. You swim in your shoes and run in your wetsuit (acquired skills, trust me). You might swim in the ocean for a bit, run over sand to get to a pond, then run on a trail to get back to more ocean, and repeat.

A hallmark moment comes at check-in when they wont give you your timing chip without showing that you have a First Aid kit that youll carry on you through the whole race. (And hopefully, carry it out again, unopened.)

First Aid kit? What do they think is going to happen out there?

Anything.

Which is one of the reasons Swim Run is starting to attract more and more participants. These races mix a little bit of adventure and off-road with traditional endurance racing, says Danny Serpico, owner and operations director of the Ignite series, which now has 5 races in the US. You dont need a compass and a map, but its not a road race. Everyones sort of taking it seriously, but having fun while theyre doing it.

The sport originated in 2002 in Sweden in a race that involved swimming to an island, running over it, then swimming to the next one and many more after that. That became the mother of all SwimRuns, till, The SwimRun World Championships 75 kilometers of race, 10 K being open water swimming and 65 of serious trail running. Less insanebut still challenging and interestingversions are cropping up everywhere, and there are now about 700 races worldwide. Theres no standard distance (since nature is one of the course designers, and youve got to go with what she wants), but a short course can be as short as 6 or 8 miles of combined swimming and running; long course is about 13 or 17.

Its fun for a million reasons, including:

And sometimes, theyre attached to you. Its a partner race, not a relay. And you have to stay within about 10 yards of your partner, so some teams choose to tether themselves together. After two races, Id say that being matched in your sense of adventure (as my team partner, Jen Langgons, and I were) is even more important than being perfectly matched in pace.

A race like this is about agility and acceptance. You have to take what the course gives you and figure out what you have inside that meets it. You might stand next to a mossy, waist-high boulder and wonder how youre going to get over it. You might swim in surf that breaks so far out its hard to get past. You might be on a trail thats practically a vertical climb. And its all amazing.

Watching your footing, figuring out where you are, swimming in chop, or figuring out the best line to the next buoy: It requires the kind of focus and intensity that wakes you up and exhausts you at the same time.

Its more trail race than triathlon. You dont go out to crush the course because as with any truly nature-based race, it can easily crush you. So theres a kind of humility that goes with the experience and the people who choose to race it.

Everybody has a slightly different setup. You dont have time for taking your shoes on and off, so you swim in them (definitely weird the first few times). You can use whatever makes your swim easierincluding paddles and a pull buoy to keep your shoes from dragging you down so muchbut theres no transition area, so anything you want in the race you have to carry on your body (its a DQ if you abandon anything on the coursealong with that First Aid kit, GPS device, and your timing chip. Thats a lot to wear, so part of the game is seeing how little stuff you can get away withand having extra pockets in your wetsuit (we wore Orca SwimRun wetsuits at Ignite Swim Run Rhode Island. Too hot at Ignite Swim Run Knoxville to wear a wetsuit).

In the two races we did in this nascent sport, all the athletes could fit in a single photo. Which makes you feel as if youre part of a (really weirdly dressed) family. Swim Run culture (and a race rule) is that you stop and help other racers if theyre hurt.

I cant say Jen and I ran the risk of being overtrained for either race we didIgnite Swim Run Knoxville and the same series Rhode Island raceas we were each training for other, different races at the time. Our transitions were rocky, at best. We didnt do as much trail running as we should have. We actually stopped at some overlooks to check the view. We were pretty surprised that we won our division (short course female team) in both races. Because for us, we were really going for the win in the see what youre made of and have the most fun divisions. And were pretty sure we wrapped those up.

Two key players with series in the American market right now are Ignite and Odyssey , although there are more and more local races that you can find with a simple search for Swim Run (sometimes spelled Swim Run or Swimrun).