They tend to be more prolific early season, before the sea warms up too much.
I doubt you'll see many (if any) for the rest of the summer.
The worst case I've seen was a few years ago in Malta in March. There was literally a 'carpet' of them all along the waters edge on the beach, about six feet deep. You couldn't get into the water without stepping on them. We didn't bother, lol.