The first one is correct if you're addressing the general public, which includes people you do not know anything about. Such a statement could be found on a warning sign next to a lake. Also, you rarely hear anyone say 'a strong swimmer', you would usually say a good swimmer. Nice and simple! 😊 When you say even though to a person you would usually be addressing just one person or a group of people and have the certainty that they are good swimmers. So for example: ' Even though you're a good swimmer, you're still at risk of drowning. ' or ' It's dangerous to swim here, even though you're all good swimmers.'

This is an instance of too many words spoiling a sentence. I wish we had context, but the best way to convey the important message in your sentence is this: "It is dangerous to swim here" The reason I wished for context is that if someone else said, "I am a very strong swimmer, so it is not dangerous for me" So then you would say, "Even though you are a strong swimmer, it is dangerous to swim here". Both of your sentences are technically correct (I agree with the other comment, I am not sure if that "you r" is a typo), but worded that way, are a bit awkward.

Is the 'r' in the first sentence a typo? It should, of course, be 'are'. The letter 'r' is not a word.