I’ve been snorkeling long enough to think I knew the water. The ocean, with its rolling swells and that electric shot of salt on my lips. The lake, glassy and still, so clear you can see every pebble on the bottom. Two worlds that feel completely different—and not just because of the fish.

For years, I treated them the same. Same mask, same fins, same carefree drop into the water. Then I started noticing something. In the ocean, I float higher. My legs drift up effortless. My breathing is easy, almost rhythmic. In fresh water, I sink. My legs hang lower. My chest sits deeper. And after a while, my breathing gets shallower. I start working harder. I thought it was just me being tired. Turns out, it’s physics—and it matters a lot more than most people realize.

Here’s what I’ve learned from the research and from hundreds of hours in both types of water. I hope it helps you enjoy your next snorkel—wherever it is—with more confidence and less worry.

Why Buoyancy Changes How You Breathe

Saltwater is about 2.5% denser than freshwater. That doesn’t sound like much until you’re floating in it. In the ocean, that extra density lifts you, making your body more horizontal. Your chest sits higher, closer to the surface. In fresh water, you’re less buoyant, so your chest sinks lower. And here’s the key: even a few inches of extra depth increases the water pressure pushing against your ribcage. At just a foot below the surface, that pressure is about 30 centimeters of water—enough to make your lungs work harder to expand.

Now add a snorkel. Every time you inhale through a tube, you create negative pressure in your chest to pull air in. The more resistance your snorkel has, the harder your lungs work. A study on snorkel safety from Hawai‘i tested 50 different snorkels and found that resistance varies wildly—and you can’t tell by looking. Experienced testers guessed wrong 74% of the time on high-resistance models. You could be using a snorkel that requires significantly more effort with every breath, and never know it.

In fresh water, where you’re already lower and your chest has more pressure on it, that extra resistance adds up fast. Over a few minutes, the cumulative negative pressure can strain the delicate tissues in your lungs. That’s how Snorkel-Induced Rapid Onset Pulmonary Edema—SI-ROPE—can happen. It’s not about water in your lungs; it’s about fluid pulled from your own blood vessels. And it starts with just feeling a little short of breath.

What I Changed in My Gear and Routine

At Seaview 180, we design our masks specifically for surface snorkeling. That’s not a marketing line—it’s a design philosophy. We engineer for low breathing resistance and good airflow separation, because we know those things matter. But no mask eliminates the risks of immersion. You still have to choose your gear thoughtfully and test it in the water you’ll actually be in.

These days, I do a few things differently:

• I test my mask in shallow water first. If I’m switching from ocean to lake, I spend five minutes floating and breathing before heading out. I pay attention to how my breathing feels. If it’s harder than usual, I check the seal and the snorkel.
• I avoid exertion. The research shows that increased effort—swimming against currents, long distances, or workout-style snorkeling—is a common factor in near-drowning incidents. I take it easy, especially in fresh water.
• I stay where I can touch the bottom. Almost all near-drowning events in the study happened where the person couldn’t stand. If I’m not comfortable in deeper water, I don’t go out.

The Air Travel Connection That Surprised Me

Here’s something I didn’t expect: researchers have found strong physiological reasons to believe that recent long flights could increase your risk of SI-ROPE. Aircraft cabins are pressurized to about 6,000–8,000 feet equivalent. That means you spend several hours breathing mildly hypoxic air. For some people—especially those over 50, or with undiagnosed heart conditions—that mild oxygen deprivation can temporarily weaken the membranes in the lungs. Then you land, head straight to the water, and ask those same lungs to handle the extra pressure of immersion and snorkeling.

In Hawai‘i, 69% of snorkeling deaths between 2017 and 2019 were visitors. The average age was in the 50s and 60s. Many had heart conditions that increased their risk. The study recommends waiting two to three days after air travel before snorkeling. I now do that every time I fly to a new destination. It’s a small price for peace of mind.

Simple Tips for Safer Snorkeling, Based on the Research

The same study that uncovered SI-ROPE also proposed ten safety tips. I keep them in mind every time I get in the water:

1. Swim at a lifeguarded beach when possible.
2. If you can’t swim, don’t snorkel.
3. Familiarize yourself with your equipment in shallow water first.
4. Always swim with a buddy and keep an eye on each other.
5. Stay where you can comfortably touch the bottom before venturing deeper.
6. If you have a heart or respiratory condition, consider not snorkeling without medical advice.
7. Check your location every 30 seconds—currents can drift you fast.
8. If you suddenly feel short of breath, remove your mask, get on your back, signal for help, and get out immediately.
9. Avoid exertion while breathing through a snorkel.
10. Wait 2–3 days after long air travel before snorkeling.

Two Different Worlds, One Important Lesson

Freshwater and saltwater aren’t interchangeable. They change how you float, how you breathe, and how your gear performs. Understanding those differences has made me a safer, more relaxed snorkeler. I hope it does the same for you.

The next time you’re planning a snorkel trip, think about the water. Test your gear. Listen to your body. And if you’ve just stepped off a plane, give yourself a couple of days to settle in. The water will be waiting, and you’ll have a much better time when you’re ready for it.