So after all these days of going to the beach, I finally brought my swimsuit and went in the water, and I had an ever so fun time. It wasn't what you'd call warm out, but since before swimming I'd biked, oh, some number miles on the path along the back beach I was ready to be cold. And the water wasn't that bad at all, once I got used to it. Best of all there were very nice waves; most of them were breaking further out than I dared to go, but even after they broke they were coming in three feet high or so (the big ones anyways) so they were still great for riding. So that's what I did. I had a fun time. I want to go back tomorrow.
One other thing worth commenting on: I didn't notice on the way down to the water, but as I was heading for home I couldn't help but note that the beach is filthy with trash. All those millions of people sunning and swimming all weekend left enough rubbish that, now that it's been distributed evenly by the wind, there's a large section of beach with a piece of trash about every two feet or so, in a two-dimensional grid. But luckily all the trash down by the waterline got washed out to sea or something, so no one has to look at it when they're swimming.
Also, a final note: we have sharks gathering offshore here in Santa Monica. Folks saw a couple of them off Will Rogers beach, where I biked to but didn't go in the water there; but I'm sure they make their way down to the Santa Monica city beach too from time to time. But that's not why I didn't dare to go in deeper. The five or six foot waves and the unknown power of the undertow was enough for that.