To people who want to learn how to react, and what to do, I can recommend the first aid courses given by the Swiss swimming rescue organisations.

You learn how to ascertain situations, apply ABC schemes (thus you would have carefully turned him over, checked consciousness, breathing, call 112, then put him in a stable side position after checking the bleeding), you also learn how to give CPR and use a defilibrator, AND you learn how to save people from the water.

I was in a group with 12 girls aged 20-22, and we were nicknamed the baywatch team . This was in Bern by the way.

website is http://www.slrg.ch/de.html
Note you can change the language of the site, and you can also look up the local clubs in Romandie.