In my book The Batavian I describe how the protagonist encounters dolphins at sea and later meets with a sperm whale. Those images are drawn from my own memory: dolphins drawing glowing tracks at night in a shining sea, and a sperm whale appearing just ahead of my ship, then diving deep, showing its enormous black tail fin.
Dolphins are often seen at sea, but in Dutch coastal waters I have never met them. Porpoises (also known as 'sea pigs'), are common though, often seen in the distance, showing their backs above the surface. But once I saw them close by. A few years ago my wife and I sailed on the Grevelingen, a former estuary closed off by a sea wall, on our way from Brouwershaven to Bruinisse, eventually bound for Antwerp. We had just departed from Brouwershaven, when I heard something snorting alongside and saw a large, streamlined black shape appear.
It turned out to be three porpoises, coming to play on the bow wave of our sailboat. I could also observe how they breathe, dive deep and emerge again. The first thing you notice is a dark shadow underwater and a bubble path indicating exhaled air. Then they pop up and the inhalation is heard as a short snorting sound, made with the nostril in the top of the head. Sometimes they remain on the surface for a moment, but usually they disappear at once.
It was almost an encounter with an alien creature, a 'close encounter of the third kind', at least a glimpse of a completely different world for which we normally do not get the chance.