There are a lot of misconceptions about being a lifeguard. Officially I am a "surf rescue technician" on the Ocean City Beach Patrol. This means nothing to anyone who isn't also on a beach patrol. What the general public thinks of when they hear "lifeguard" is: chill-ass job bronzing in the sun and picking up girls. There are also some sweet stereotypes that are, really, mostly true. Eg: frat bro down for the summer, surfer bro, a bro in general. I am a rare exception. Somehow i'm a somewhat self-aware philosophy bro who enjoys, well, everything in life and has a strong sense of childlike wonder about things.
I digress, back to misconceptions. In actuality surf rescue is a high-stress job in which you are responsible for hundreds/thousands of people at any given time for x blocks north and x blocks south of your tower. And it's not just the water, it's the beach. You are responsible for that area where people have strokes, heart attacks, umbrellas impaled through them, pipe bombs, heat exhaustion, and other emergencies.
And the ocean. It isn't a pool. Nor is it a lake. It is the ocean. The ocean is not a consistently calm and predictable entity. It is dynamic and changing, driven by the changing weather. There are also things that exist called sea life and they play in the ocean too. They are mostly pretty chill given the circumstances (thousands of people peeing/spitting/pooping/spitting/dominating their near-shore chill zones for 4 months every year), but sometimes they get unhappy or decide to play a joke on people. People don't like jokes nor do they like sea life because they don't like that they are paying to be at the beach and in the ocean and the sea life gets to chill for free. It just isn't fair. Most people get revenge by eating the larger fish and the crabs that they hate to swim around and step on at night.
So ya, the ocean isn't like a lake or a pool. It has a bottom made of sand (at least here, in Maryland). Sand shifts very easily. Waves are wind energy transferred into the water. The harder the wind blows and the longer the distance it blows over the more powerful and larger the waves. Once the wind energy becomes wave energy it is known as 'swell'. Most vacationers in the summer don't get to see hurricane swell or even any significant swell at all because summer tends to have long flat spells (small waves) via not a lot of active weather. Big waves come from big storms (low pressure, you know, those things that give us widespread snow and rain and wind) and not so much from small storms (thunderstorms in the summer are isolated events, they are from localized imbalances, not widespread at all). Where am i going with this? K. here we go: Waves are energy, simply traveling through the ocean as their medium. Energy. Pure energy. They travel until they interact with something that causes them to disperse their energy. Cue sandbars. Energy comes in, feels itself against the ocean floor, and the top of the wave topples. The energy is directed at the sandbar and is dispersed across it as the sand particles absorb and scatter. This process occurs endlessly.
Occasionally a sandbar will collapse and form an underground trench. As waves come in and suck back out the water takes the path of least resistance out. Since water will flow through the lowest lying area first they suck back out through this trench, widening it. We now have an underground river forming, aka a rip current. This is what people get stuck in and usually drown if they don't know what to do/panic when we are off duty.