There are a variety of reasons why it's considered best practice to make people have a shower before entering the pool. They already explained it, talking abou

There are a variety of reasons why it's considered best practice to make people have a shower before entering the pool. They already explained it, talking about elderly people / etc. If it's sunny and you are out of the water from three hours tanning, your heart adjust to a certain frequency. If you jump in with any prior advice to your body into the water, heart has to adjust to a much different frequency, and an heart attack is possible. The problem here is that a lot of people doesn't know what's going on with their hearth and certainly a lifeguard doesn't know about. Also, adding to that, https://en.wikipedia.org/wiki/Cold_shock_response https://en.wikipedia.org/wiki/Cold_shock_response I don't know about Sweden situation, but it seems really weird that no lifeguard was there. In Italy every public or private place with a pool needs a number of lifeguards according to the number of people of the pool / the pool's dimension. It's really easy to have some heart attack or hypoxia going unnoticed, example: X person jump in, simply doesn't get up. Also, time is key, if an heart attack occurs a close defribillator with someone able to use that / a lifeguard able to transport that person out of the pool without damages (it's not that easy as it sounds) can be really important. Drowning situations are even more dangerous, a drowning person can have a force in their arms able to do real damage and everything needs to be deal in the safest way.