So you put on a wet suit. I think the ladies can imagine this best: it is like a slightly stretchy pair of very thick panty hose that cover you from ankle to neck. I also have a hood and gloves, making the only part of my body really exposed to the freezing water my ankles (my feet are encased in my swim fins).
With your loins properly girded (whatever that means), you jump in the water... and the suit begins to fill with ice water (it is a wet suit)... from the ankles up, and more importantly, there is a trickle of ice water running down your back.
Your. Heart. Stops.
Finally, the water in the suit gets heated up by your cooling body, and a kind of equilibrium is reached. Your heart restarts (at least so far it has every time), and you breathe like a hard-ridden race horse.
Then you go to work - take the allen key down and fit it into the screw holding the spent zinc (DO NOT DROP the key). Break it loose, and turn it out. By now, you have made perhaps 4 trips down, resurfacing to get more air in between. Finally, the screw and the zinc are in your hand. Place them on the dock, and take the new zinc with the new screw pretreated with Locktite (thank you, Jane!). Breathe deeply and submerge again, attempting to start the screw good enough to leave it while you surface again for air. Maybe you get it, maybe you don't. But you cannot make a mistake - the water is 25 feet deep here - out of reach for me - do not drop anything your are holding in those thick stiff rubber gloves. Another few trips and the screw is tight, and you are done. Yes, you have indeed earned that beer, after you strip off the wet suit in the shower and warm up.
And because it was the first really nice evening of the year, a dock party formed, so the evening had a perfect ending, sharing food, and drinking beer with friends as the sun went down.
Here's the zinc I removed, compared with a new one. It was definitely time for it to go. And now I can look forward to warm weather, dread-free.