cote those statistics you've quoted lack information that tells us why those people drowned. Therefore, they are not very useful when it comes to assessing risk.
They suggest that most of the 300 people who drowned (188) expected to be in water, otherwise why make the distinction between those who didn't expect to be in water (112)?
104 of the people who drowned were partaking in water-based activities. It doesn't say how many of them could swim but it's a reasonable assumption that some of them could. And yet they still drowned. There's no information to explain why.
I don't understand the relevance of saying that 77 of the people who drowned were out walking or running. They might have been but fancied a dip or gone into the water to save a drowning person or a dog. It's a reasonable assumption that, like the other people who didn't expect to be in water, some of them would have been able to swim. But again, the report doesn't explain why they drowned.
The 35 people who died from suspected natural causes while or after being in the water might have also been able to swim. I'm guessing that some of them might have had a heart attack while swimming or died from hypothermia after a shipwreck. But again, because the report doesn't explain, we don't know.
Being able to swim is a good thing for a number of reasons, one being that it might save your life. But it might not - as the figures you've linked to appear to show.
Therefore I don't think swimming is any more of an essential life skill than being able to grope your way out of the dark in a smoke-filled building.