It is difficult to just go for a swim in Lugano. I was only aware of one public beach that was on opposite end from Paradiso. Your options are to pay to access a private beach connected to hotel or such.
So we went here, after 5pm (so it was much cheaper). There are running, screaming kids around the pool area, but the beach was a bit calmer at this time of day. The water is great for swimming but I have one warning - STAY OFF THE RAFT! I swam out to the raft and relaxed there briefly. Within two days I had ringworm (a fungal rash, not a worm) on my back, along with a large area of rash presumably of a fungal nature.
I personally would not return.