Some safety advice
Here are some safety advice to enjoy your snorkelling sessions:
Snorkelling adept, cold is your sworn enemy. You will need to have the best equipment possible (the body cools down 25x more quickly in water than in air...). Neoprene wetsuits, shorts and tops will be your allies to practise in these cold conditions.
Neoprene has a great buoyancy factor, this makes the wetsuits and other neoprene clothing a security item as well. You can use floating pool noodles to increase your buoyancy.
You have to be hydrated and fed with slow burning carbs. This will protect you from cramps and sudden tiredness. Don't forget to stretch after a snorkelling session, like for any other sport activity.
Tell to others where you are going and never go alone. If you are practising regularly, you can use a small signal buoy on the surface to mark your presence, to avoid accident or signal your position in case of one. A buoy is ideal if you want to take drinks or cereal bars with you.
To protect the fragile environment around you, don't bring any food for the local fishes, don't touch anything and mind your fins. The conservation of these environments rests in your hands.