Hanauma Bay is a jewel in East Oahu, a marine preserve perfect for snorkeling that attracts about 1 million visitors a year who are eager to ply the turquoise waters. Hanauma Bay is not as placid as it seems from the picture-postcard view just off Kalanianaole Highway, however, and snorkeling is not the relaxing, carefree pastime that some tourists imagine it to be.

Twenty-three people drowned at Hanauma Bay from 2004-2013, 22 of whom were visitors, according to "Drowning and Aquatic Injury Trends in Hawaii," a report by the Department of Health. Snorkeling was the most lethal ocean activity in the entire state, according to the report, with tourists far more likely than residents to die doing it.

The latest victims are a couple from Washington state who died while snorkeling at Hanauma Bay on Friday. The circumstances of this most recent tragedy demand a frank reassessment of the lifeguard staffing levels and tower locations at the bay.

The site is a safety challenge partly because it is so busy — about 3,000 people visit each day the bay is open — and because the sea of snorkelers are face down in the water, making it more difficult to instantly discern who is in trouble.

There were eight lifeguards on duty that morning, including stationed in a tower at the top of the bay. However, the victims — a 60-year-old man and a 55-year-old woman — were not spotted in distress by any of the lifeguards, but by a hiker who apparently had a better view. The couple were struggling about 600 yards from the main beach, beyond Witch’s Brew, a cove on the Ewa side of the bay that is not off limits to visitors.

It is past the reef break, and the water is 10 to 20 feet deep. Once alerted, lifeguards brought the couple ashore on a rescue watercraft, but it was too late.

The rocky area that forms the Witch’s Brew cove juts into the bay, and the outcropping may have obstructed lifeguards’ line of sight. If that proves to be the case, the area either should be deemed off limits to swimmers and snorkelers or lifeguards should be added or repositioned to cover the area. Rescuers cannot save someone they can’t see.

According to the DOH report, 65 percent of the people who drowned in ocean waters off Hawaii during the time period reviewed were older than 50, a profile fitting both of the recent victims from Washington state. Before walking down to the beach and the water, visitors to Hanauma Bay watch a short video that includes information about protecting the marine life at the preserve, including the reef, and some water-safety information.

The video should be intensified even more to emphasize how strenuous snorkeling is, and to advise visitors to know their limits, and stay close to shore and within view of the main beach — that line of sight goes both ways. Warnings should explictly state the increased risk for folks over 50, especially as Hawaii’s tourist demographic ages along with the baby-boomer generation. Stepped-up warnings must be offered in many languages, of course; of the 23 people who drowned at Hanauma Bay from 2004-2013, 16 were from other countries, according to the DOH report.

The vast majority of visitors to Hanauma Bay have a wonderful, memorable, safe time. Hundreds of others do get into trouble and are saved by lifeguards; there were 524 rescues in 2012, according to the Department of Emergency Services. When things go horribly wrong, as they did last week, DES must figure out why and redouble its efforts to prevent future tragedies.