After watching (incredulously) someone require rescue in two-foot waves at the beach at Burleigh, and the antics on the reality television show 'Bondi Rescue', it has come to my attention that many people are unfortunate enough to have been born inland, away from the coast, and often get into trouble in the ocean due to their lack of experience. And not just swimming or surfing - rock fishing has, in fact, one of the highest fatality rates of any sport in Australia, due to the number of people who get swept off the rocks into the ocean. Here then, is some practical advice in how not to drown.
The Basics
So, you have arrived at the beach. Firstly: can you swim? This is rather vital. Although it is possible to wade around the shallows, I really wouldn't recommend this unless it is very calm.
Secondly: are there other people nearby, in the water? Swimming by yourself is quite dangerous, even if you are the prime minister. Ideally, there would be a lifeguard on duty and a flagged safe area. Otherwise, a surfer or strong swimmer will usually be glad to come to your rescue, especially if you are young and good-looking.
Thirdly: are you protected from the elements? If it's sunny, wear sunscreen. You'll still get burnt in the water. If it's cold water, consider a rash vest, wetsuit top, or full wetsuit. Rain doesn't really matter (you're getting wet anyway, after all), but wind chill can be very significant - often the air can seem much colder than the water.
Finally: if you get in a bad situation, Don't panic. Cannot stress this enough. The first time you are in the path of a big wave (and big rogue set waves have this inevitable apocalyptic feel, they darken the horizon) you will think AAAAAH SHIT SHIT I'M GOING TO DIIEEEEE. After a while, you'll learn that you do not, in fact, die. Remember that you're looking up at the wave from the surface of the ocean, and it looks much bigger than it is, in the same way as furniture and doorways look bigger when you're lying on the floor.
Waves
A swell in the ocean, or wave just about to break, moves water in a circular motion: back, up, forward, down. Although it can feel otherwise, a wave doesn't really move you, but leaves you in the same place.
A wave breaks when the water gets shallow enough that it can't find any more water 'underneath' it. The wave face steepens and then collapses or throws outward. Usually this is when the depth is about the same as the height of the wave, although it can be much shallower. The projecting sheet of water is called the 'lip'. Depending on the gradient of the ocean floor, a wave can break as a gentle spill, picturesque hollow tube, or fearsome gurgling warped monster.
After a wave breaks, it collapses into in a bouncing mess of foam called the whitewater.
The ocean will alternate between occasional sequences of several large waves, called 'sets', and periods of relative calm, called 'lulls'. If you're venturing out past the breakers, endeavour to do it during a lull.
Wave power grows exponentially with size. A six-foot wave is many times more powerful than a three-foot wave, which is many times more powerful than a one-foot wave. And if you get hit by a powerful wave, you'll be certain it was cement, not water. Respect the ocean.
The way to avoid waves is to dive underneath them. The turbulent zone of whitewater especially only extends a few feet under the surface. Dive nice and deep ('grab a handful of sand' as they used to say in junior surf life saving) and wait for the wave to roll over the top of you.
Advanced: Just after a wave breaks, right when you'd expect the force to be greatest, there will be a low-pressure zone that allows you to duck under the wave very easily. This is caused by the lip 'bouncing' off of the surface. This is a get-out-of-jail free card when you get caught out by a big set.
Rips and Currents
In general, rips refer to areas where water is moving from the beach out to the ocean, while a current is a movement of water sideways along the shore.
Rips get a bad and scary reputation, but in actual fact surfers love them. They are the escalators or ski lifts of the ocean: you sit there and it whisks you out to sea, saving you the effort of actually paddling!
Rips tend to gouge out channels of deeper water, preventing waves from breaking, and are often deceptively calm. It's safer to swim where there are lots of waves breaking, than where it is calm.
Two important things about rips: firstly, they stop once they get past the breakers. A rip isn't going to suck you kilometres out to sea. They very very rarely extend more than a hundred meters from shore. Secondly, you can't swim against a rip. You'll just tire yourself out. Give up, and either swim across it, to the side; or concentrate on staying afloat, and wait until it carries you past the breakers and it dissipates. You can then swim back to shore a little way down the beach.
Currents will carry you across the shore, rather than out to sea like a rip. They are more of a nuisance than anything else. Just remember to keep an eye on a landmark on shore and make sure you aren't drifting too much.
A very common pattern of water movement is a current pushing down the beach, into the bay or corner next to the headland, from where it will turn 90 degrees, become a rip and push out along the rocks. Watch out for this.
Tidal Currents in River Mouths and Bay Entrances
Now, rips and currents on an open beach can be powerful, but tidal currents at the mouth to an inland body of water can be truly frightening forces of nature, and unlike rips can carry you a long way out to sea. At high or low tide, it will be calm. Halfway in between, there will be a lot of water moving. Be careful, and avoid going in the water when it's not dead high or dead low tide.
Rocks and Reefs
Unless you're dealing with fairly critical surf, water is kind of soft, and a sand bottom won't give you anything worse than a touch of gravel rash. Rocks and reef bottoms, on the other hand, are extremely solid. If you get pushed into a rock, you're going to get cut. If there are barnacles on it, you're going to get really cut. Submerged rocks and reefs are the most immediately dangerous objects in the surf.
If the beach is rocky, or there is only a small strip of sand, it's very likely there will be submerged rocks. Some will be deceptively covered in a few centimetres of sand. Tread carefully and lightly when wading. Reefs have all manner of nasties - coral, sea urchins, blue-ringed octopuses, stonefish. Any surf break over rock or reef should be treated as black diamond difficulty.
Ever since I slashed my right foot open horrifically on a barnacled rock at a Shellharbour reefbreak a few years back ("It's deep enough for stitches, but the gash is too wide" observed the doctor), I've taken to wearing a pair of neoprene wetsuit booties, which also make excellent footware for sailing or boating.
The Black Art of Rock Jumping
Once a upon a time, sick of the tiring effort of paddling out to the breakers through the whitewater, a lazy surfer thought "Why don't I just run out along the headland, and jump into the ocean off a rock?". Thus was born the dangerous art of rock jumping, or 'rocking off'. It involves dashing out during a lull, negotiating a rock shelf that is alternatively slippery with moss and razor sharp with barnacles, and then jumping over a wave as it breaks over and floods the slippery/sharp platform with a waist-deep surge, hopefully being whisked out to sea on the back-draught. It's as dangerous as it sounds. Really, really don't try this until you've watched someone else go first.
Other Hazards
People, surfboards, and other surfcraft
You do not want to get hit by any of these things. Be very careful when the surf is crowded. Surfboard noses are very pointy and fins are quite sharp, especially when propelled with force into your face. People are squishier, but can get angry. If you surfboard ends up impaled on a fence post above graffiti proclaiming "LOCALS ONLY! k00ks gEt FARKeD", you've clearly collided with the wrong person.
I won't really get into detail about surfing etiquette in this node, but will note that it is your responsibility to get out of the way of someone riding a wave. If they run into you, it's your fault. That's just how it is, and once you start trying to ride waves yourself, you'll appreciate how difficult it can be to steer around a swimmer. The best way to avoid a surfer is usually just to dive deep.
Seaweed
Not dangerous as such, but it's icky, and stinks to high heaven when it's washed up on the shore and drying. Big swells or storms will rip it off the rocks and cause it to be everywhere for a few days. Tends form large rafts. Avoid.
Sea Creatures
You will not get eaten by a shark. I repeat, you will NOT get eaten by a shark. I guarantee it. If you do get attacked, and as a result feel that I lied to you, message me and I will pay you the sum of $100. I've never seen one, although I know friends that have.
A much more mundane danger is the Portuguese man-of-war, a.k.a. the bluebottle. It's a blue jellyfish-thingy that floats on top of the water and will give you a nasty sting. They look like big, iridescent blue bubbles, and the tentacles extend for a few meters so give them a wide berth. I've been stung a few times, and it's comparable in pain to a bee or wasp sting: nasty, but not really a huge deal unless you have an allergy. Or unless a tentacle wraps around your throat, which has been known to happen. (A fun game is to try and pop bluebottles that are washed up on the beach without being stung).
You might see dolphins. On the east coast of Australia (even on Sydney beaches), they are relatively common, and often swim up really close. This is a magical experience. They are good luck, as it is well-known that sharks are scared of dolphins (seriously, dolphins attack sharks).
Fish are just sort of there, and aren't really that exiting. A couple of times, when I've been sitting on my board, a crab has mistaking the nook behind my knee as a rock crevice or something and tried to crawl in there. For a while, there was even a resident penguin at Mona Vale beach.
Worst-Case Scenarios
After jumping over a wave, you try to stand, and realise you can no longer feel the bottom. You look to shore to find it an uncomfortably long way away. Firstly, don't panic. You are in a rip or current. Wave your arms around and yell to get someone's attention. Relax and concentrate on staying afloat, and if you feel strong try to swim across the rip or current to get out of it.
While fishing on a rock shelf, a freak wave appears and sweeps you into the ocean. Firstly, don't panic. Shed bulky waterlogged clothing (actually, avoid wearing it in the first place). Try to swim for the beach, or a sheltered inlet or cove with a gradual bottom, with an aim to clamber back up onto the rocks. If you get caught in front of a breaking wave on a shallow section of reef, dive down and try to 'starfish' on the rocks by grabbing tightly onto the ocean floor. Wave your arms around and yell to get someone's attention.
While surfing a fair way out to sea, in a moderate to large swell, your legrope breaks and leaves you without a board. Firstly, don't panic. Swim for shore, but not too quickly, don't tire yourself out. Try and get yourself caught in whitewater and let it push you towards shore. (Having a surfboard or bodyboard does not make up for being a poor swimmer. Expect to lose it at some point, and always be able to swim back to shore).
Having caught a small wave a little way into shore, you turn around to paddle back out, only to find the monster set of the day about to break on your head. Firstly, don't panic. Throw away your board, trusting to your legrope to keep it attatched to you (first making sure there's no one behind you who could get hit). Relax, take deep breaths and dive deeply under the waves. Once the set has passed, there will be a lull. Rally, recover your board, and paddle back out as if nothing had happened.
One of the above happens, but there's no-one around. Endeavour not to be in this situation.
Conclusion
Hopefully, you are now slightly more prepared to tackle the surf. Remember, like any wilderness, the ocean is a hostile environment and needs to be treated with respect. Don't underestimate it, don't get into situations beyond your ability, and don't go alone or take rescue for granted.
But seriously, whether you're bodysurfing, bodyboarding, traditional surfing, or just swimming, it's a bunch of fun, and the challenge and man-against-nature aspect is part of that. Get out there!
Edit: In a bitter-sweet coincidence, less than a week after I wrote this, my dad (who's been a surfer, professional diver and boathand for much of his life) rescued an elderly man off a beach in Port Macquarie. He made the local paper and everything. He said he was surprised at how heavy the man was, and how hard it was to keep him above water. The man was unconscious by the time they got to shore, but he lived.