On yesterday's dive at the quarry my buddy and I frequent, we took along kitchen scrub brushes for our final deco stop. We staged the brushes at a training platform, and once we got there, we killed time and ran down our deco scouring off the accumulated algae.
Lots of crud came off, and we did our best to wave it away. But of course, a goodly amount of loose algae rained back down onto the platform's surface. That annoyed me. So I decided, "hey, I'm wearing big-ass tech fins that move lots of water, so all I need to do is flutter-kick vigorously as I swim overtop, and I'll blast all that crud to kingdom come."
Yeaaaaah... When I put that plan into action, the backs of both my legs, from the thighs down through the calves, all the way to the ankles, spasmed into a single massive cramp.
Lesson learned: Don't do that again.