I can.
I think.
At least I could the last time I was in a pool or lake.
Not sure I ever could in an ocean.
I taught my kids to swim. They swam in the pond here.
Grandkids went to swim classes at the pool.
No swimming in the pond allowed anymore. But I wanted them to know how in case they fell in.
The babies have had drown proof classes. They will take actual swim classes this summer.
Can you?
I cannot. Can probably float.
Of course. To me, the question is almost on a level with “can you walk?” It seems incredible to me that anyone will say no, but I know they will. My mother-in-law was a non-swimmer, and she drowned.
All right, she didn’t drown, but she could have!
I’ll teach you if the opportunity ever comes up. I’m sure you can do it!
I was a US Navy enlistee; being able to swim is a requirement. 
I grew up on a Great Lake. I was swimming before I was 4 years old.
Since I was a baby, yes. Learned in my parents’ kitchen sink in point of fact, and early in toddlerhood had no issues; they would mount a float on my back and let me do my thing.
So did I, but it was some time in my teens before I could swim, and I’ve never been very good at it.
Well, perhaps not quite as ON the lake as you; it was maybe a ten-minute walk to the beach, whereas IIRC, your stately ancestral home includes a bit of the shore itself?
Yes I can. I’m not a strong swimmer in terms of technique but I do know how. I also float with little effort.
I still use a pfd when kayaking though!
My husband is a strong swimmer, and my son has been taking lessons since he was little. He loves to swim.
There are so many lakes and rivers around here (and Canada in general) and so many people have backyard pools that I’d consider it irresponsible to not teach a child to swim. Sadly there are still several preventable drowning deaths every year.
I grew up on the Riverine Plains of NSW with no permanent lake or river within 50 miles. Yet every primary school had “Learn to Swim” programs taught in dams or channels and then formalised with certification from swim classes in the town pools. Maybe not by 4yo, but 6yo, yes.
Oh yes, a nice sandy beach with right of exclusive use down to the waterline. The lake only tries to eat our house every 2 or 3 decades
I’m a fairly good swimmer. I learned taking classes over the summer at my elementary school. I recently swam in the ocean for a few hours on a cruise to the Bahamas with no issue other than a nasty sunburn.
I do have issues where I can get blinded if I get saltwater (or any water) in my eyes, so I have to be careful to avoid that. I don’t tend to dive underwater much because of that.
Nope.
My parents tried. I had lessons three times as a kid: once in a big group of kids (I was probably 6 or 7), and twice more, with private lessons. Each time it was attempted, everything went well, until the time came to put my head under water, at which point, young me would panic.
I never went back to it. Any time I’m on a boat, I make sure to wear a life vest, and I try to not put myself in positions where I might accidentally wind up in the water.
When I was a toddler I toddled away from the kiddie pool and jumped into the deep end of the big pool. That was the point where my parents took special care to make sure I would properly learn to swim. I got pretty good at it.
The Lil 'Wrekker had trouble with the head under the water as well. Finally she did it.
She swims now but is still leery.
I’ve swam since very early, I don’t remember how I learned.
I swim just fine, though I think I lack the dive reflex so I have a hard time going underwater without plugging my nose. Otherwise fine.
My son has been in private swim lessons for a little under a year and it just feels like aaaagonizingly slow progress. He’s so close to a number of target skills, but he doesn’t like to put his ears underwater.
He did graduate from a three-pack floatation device to a two-pack, so that’s something.
It’s so expensive and I have to get up at 6am every Saturday to take him. Just swim, kid.
Yes. When summer comes around I do laps in the complex pool almost every day.
I learned to swim in a simple pool. I’ve never been in a complex one.
The idea that “every time some swimming teacher made me put my head underwater was terrifying, but maybe it won’t be so bad next time” never entered into my head as a kid. Plus, I was a nerdy, indoors-y kid, and never really had any interest in swimming.
I should also note that, as a kid, I was very skinny, and probably couldn’t float. Now, I probably have enough body fat that I could pull off floating.
About a decade ago, a friend of mine decided to take up the challenge with me. We spent an afternoon at a pool, and with a few hours of acclimation, she actually was able to get me to go completely underwater, and even open my eyes, without panicking. it was pretty novel, but I still have no interest in swimming. 
I don’t float. I just don’t. I’ve had good and bad teachers try with me, and the problem is ultimately me. I had a lot of bad childhood experiences with water and my fear of the water is always going to be stronger than my desire to swim. I just don’t care enough to force myself to get over it.