It is very important to be aware of the Portuguese Man O War, a jellyfish like sea creature, which you may see washed up on the beaches.  At first glance it looks like a small, transparent, inflated cellophane wrapper, but beware.  They can give agonising stings even when dead, and should not be touched.  Many people are not warned about these enough, and that it is unadvisable to swim in the sea if  they are seen washed up on the shore.  Their dangerous parts are their tentacles which are very long, and if stung, medical attention should be sought.  Not so much of a danger at private beach clubs or beaches where there are manned stations, as the appropriate warnings will be given, they should be watched out for early in the season on public beaches, and beaches not frequented so much.