waives the monthly maintenance fee. "20/20" continues. Here's Reena ninan. Reporter: With the sun finally shining and summer on the horizon it's time to hit the water. And these are the young men and... See More
waives the monthly maintenance fee. "20/20" continues. Here's Reena ninan. Reporter: With the sun finally shining and summer on the horizon it's time to hit the water. And these are the young men and women charged with protecting our lives while we swim. Lifeguards. Buff, busty and brave, ready to jump in at the first sign of danger, right? Well, maybe not always. Sure, they may look hot in their signature red bathing suits, ripped abs and tanned torsos like on "Baywatch." But what do we really know about the dudes and dolls behind the shades? ? it's the start of swimming season and you're outing secrets that people don't want to know. Meet 23-year-old Harris, a former lifeguard at several pools in Texas. Tonight he is blowing his whistle on the secret practices that he says sometimes occur high atop the lifeguard stand, and we do mean high. Are lifeguards using drugs? Yes. There were a couple of lifeguards who smoked weed before coming into work or they would be still rolling from the night before. Reporter: That's something many lifeguards confessed to us. And according to Harris, at one pool not only were lifeguards coming in hung over, they would blaze up right on the job. They'd check chemicals. Checking chemicals? It's a code word? Yes. Normally when you check chemicals it's to check the ph, but what they were doing is they were going back and smoking weed. Reporter: But there were kids whose lives are potentially in your hands, and they're getting high? Yes. It's very irresponsible. Reporter: It's doubly troubling, Harris says, because actually checking the chemicals is really important to keep the pool sanitary. As they say, what happens in the pool stays in the pool. If you're going to the pool, don't go at the end of the day because it's full of urine, and it's really quite nasty. Reporter: Oh! How do you know that? You can tell by the color. At start of the day it's really, really blue, and at the end of the day it's, it's more yellow. Reporter: Ick factor aside, discolored water can pose a more hidden health hazard. It makes it harder for lifeguards to see people. Take the tragic case of mom Marie Joseph. Look at this security video. That is Marie coming down the slide. Her head bobs above the water for a moment before she sinks to the bottom of the pool. Multiple lifeguards were on duty including this one directly in front of her. I just don't see how they missed it. Someone wasn't doing their job. Reporter: But the water was so murky, none of them noticed her submerged body. See here as the pool went from blue to dark green. An investigation later revealed that a pool manager held off on chlorinating the water to reduce costs. This photo shows children swimming in the pool 24 hours after she drowned. Joseph's body wasn't discovered for two days. Water's really strange. Either you're having fun or you're dying. Reporter: Roughly 4,000 Americans drown each year. And one in five children who drown in swimming pools do so with a lifeguard present. It's silent, it's quiet and it's sudden. Reporter: Kathleen pluchinsky's 4-year-old son drowned at this ritzy country club pool. She believes too few lifeguards are trained properly. I've talked to hundreds of guards, literally, and I ask this question. How many of you feel like you would recognize a swimmer in trouble immediately? Not one hand has ever been raised. Never, not one. A lot of lifeguards, they're not prepared for something really bad happening. Reporter: And here's the thing, it's actually quite challenging to spot a kid drowning, as I found out for myself with a test dummy named Timmy. I've got my underwater camera. They are going to hide Timmy somewhere in the pool. I've got to find it. How hard can this really be? Timmy is right at the edge of the pool just feet in front of me, a spot where many young kids called wall huggers drown. I scan the pool over and over again and can't find him. I never saw it. Getting ready to start an aquatic facility operational audit. Reporter: Meet rac Carroll. He is no ordinary water park guest but rather an undercover boss. The head of Ellis & associates, a lifeguard training company. Today he's here at an indoor water park in Pennsylvania, playing a game of cat and mouse with his trainees, armed with a video camera, to secretly see who's paying attention. We want to be able to see a guest in distress within ten seconds so that we're not being reactive to a situation where somebody may already be on the bottom. Reporter: Carroll does this regularly because frankly his video archives are awash with examples of lifeguards behaving badly. Look at this lifeguard totally tuning out the pool. Listening to his iPod. No lifeguard should ever be provided any electronic equipment. Certainly no texting or talking on the phone. Reporter: This guy seems to have something else on his mind besides safety. He's looking everywhere but at the swimmers. Is he checking out that woman's behind? Worst of all may be this guard. He's gone into full hibernation mode. Fortunately no one is swimming. Let's hope he returns from la-la land before some kid cannonballs into the deep end. But secretly surveilling the guards is only step one. Carroll also conducts surprise vigilance drills. Can lifeguards spot Timmy in ten seconds? They have become superb at the drill. The average response time is three seconds. We're not just people who just tan, you know, big macho people with their shirts off. We're actually like, we're saving people's lives. Reporter: But Harris warns that's no reason for parents to mistake the pool for day care. Parents will drop their kids off at the pool and they don't have any supervision except for the lifeguard. Reporter: So, parents think you're just a cheap babysitting service? I guess. Reporter: And not only do kids need to be monitored constantly, rac Carrol says so do the guards. But isn't it uncomfortable to have to go to the lifeguard or the manager and say, "Sorry, I don't think he's scanning the pool?" It may be uncomfortable, but it's a whole lot more comfortable than dealing with your child being on the bottom of the pool.
This transcript has been automatically generated and may not be 100% accurate.