Swimming outdoors in not like swimming in the relative safety of a swimming pool with Life Guards and predictable water - it is a risky activity . As with all risks if you use common sense and gain some expertise and knowledge those risks can be mitigated.
The first rule to remember is that the water is never to be underestimated - always make sure that you swim well within your capabilities and make sure before you get in that there is a safe way of getting out. If you're at all uncomfortable with the conditions leave it for another day - the sea will still be there tomorrow ..........
Tides and weather are a big influencer as to whether or not it is safe to swim so I've added some general information here but please read up further and never, ever, swim if you don't feel comfortable with the conditions.
Take no heed of what other folk are doing or telling you you can do - you must make your own decision based on your own ability and confidence.