On a typical Monday afternoon, Hanauma Bay is filled with snorkelers of all ages, faces immersed in the ocean, searching for fish and coral in the nature preserve.

The bay, which hosts nearly 1 million visitors a year, is featured in online videos and travel sites as a family-friendly destination but is also home to the highest number of drownings on Oahu. While that’s due, in part, to the sheer volume of visitors, it’s also because snorkeling is the most common activity in ocean drownings in the state.

“At least every day we average four to five rescues, some days more, some days less,” said Lt. Kawika Eckart of Honolulu’s Ocean Safety and Lifeguard Services.

Between 2007 and 2016 there were 169 snorkeling-related drownings in Hawaii out of 650 ocean drownings, according to state Department of Health figures. Most of those snorkeling deaths, 156, were nonresidents, far outnumbering the next-highest cause of nonresident deaths from motor vehicle crashes at 85 in the same period.

A state committee is exploring ways to help prevent them.

In Maui and Kauai counties, snorkeling was the No. 1 cause of ocean drownings among visitors, with 72 and 20 incidents, respectively, during the same 10-year period. On Oahu, swimming was the top cause of ocean drownings at 70, with snorkeling coming in second, with 58, during that same period, with 16 of them at Hanauma Bay.

On Oahu so far this year, 16 ocean drownings have occurred, with one of the most recent being a 27-year-old male who was reported to have gone snorkeling alone at Kaimana Beach in Waikiki.

“More novice swimmers or people without any kind of ocean skills tend to go snorkeling because it’s looked on as a really safe activity,” said Eckart. “You’re not getting into the surf. You’ve got fins, a mask and snorkel on … so there’s a false sense of security.”

Snorkeling is actually a strenuous activity, he said, particularly for beginners and those with pre-existing health conditions or limited swimming skills.

In a recent effort to educate visitors, Honolulu Ocean Safety teamed up with Real Hawaii TV to get public-service announcements into 25,000 hotel rooms on Oahu. One of the messages is to always snorkel with a buddy.

That same advice is offered toward the end of a nine-minute video that visitors are required to see at the Hanauma Bay education center before going in, which also warns people of sudden drop-offs on the ocean floor.

But many visitors who visit the bay are still caught unaware.

“It’s amazing that more people don’t get into trouble,” said Eckart, who has more than 30 years’ experience lifeguarding.

A typical scenario is for novice snorkelers to start in the shallow part of the bay where their feet can touch bottom. Then they start to venture a little farther out, looking for fish. Some drift to a point where they can no longer touch bottom, and then panic sets in.

“And that’s when we gotta react,” he said. “We don’t wait. More than likely, they don’t yell and scream for help. They’re just kind of freaking out and trying to get to some place that’s shallow, trying to put their feet down.”

Some lift their head out of the water but end up dipping the tip of their snorkel tubes back into the ocean and sucking in water. “Sometimes we go up and all we have to do is pull that thing out of their mouth,” he said.

The bay has three trouble spots: a deep water hole on the left, the center of the V-shaped reef straight ahead and two buoys marking the channel leading out of the reef. Snorkelers not paying attention easily drift beyond the buoys on currents but are not strong enough to swim back to shore.

“It’s easy to get out, not realizing (the currents are) a lot stronger than they thought,” said Eckart.

In addition, there are all kinds of new snorkel sets hitting the market, including trendy, full-face snorkels, which have different breathing and draining mechanisms that present new challenges.

Dr. Philip Foti, a member of the state’s Drowning and Aquatic Injury Prevention Advisory Committee, is examining different types of snorkels to determine which, if any, potentially pose a risk. He has a hunch that some do but said, “We do not know the answers yet.”

To collect data, Honolulu Ocean Safety began recording types of equipment used among drowning victims about 18 months ago. Foti, meanwhile, is developing a device to measure the oxygen flow within the various types of snorkels.

Cory Scott, a visitor from Boston, said he was surprised to learn of the drowning statistics after a day at Hanauma Bay. “I guess if you stayed in the shallow water, you’re fine. I can see if someone’s never snorkeled before, that’s not a great place to go. It’s not a beginner’s spot,” he said.