It is important to swim because if there is a flood it might take you out to sea and you will need to stay afloat or swim back to shore.
Another reason is because you might fall off a boat or the boat might sink and you could drown.
One day at the beach you might get caught in a rip and go far out to sea. Being able to stay afloat might help you to survive.
New Zealand is surrounded by water and people enjoy water sports like swimming, jet boating, kayaking and surfing. You need to be able to swim, so you can survive in and around the water.