These situations have always generated mixed reactions for me — I'd rather see the animals alive and well, but it's an opportunity to learn more about a species that we don't get to see up-close very often.
Here are views from above and from the side. The porpoise was between 5-6 feet long, the maximum length for a Harbor Porpoise.
Whenever I talk about porpoises, the question often comes up about how to tell the difference between a porpoise and a dolphin.
There are a few characteristics that are generally useful (but not always, because of some exceptions) — like a blunt snout, rather than a long, pointed snout:
And a short, triangular dorsal fin, rather than a taller, falcate dorsal fin:
But one of the best characteristics (although it's not a great one if you're watching a swimming animal!) is the shape of teeth. Porpoises have flattened, spade-shaped teeth, while dolphins have sharper, conical teeth:
When ocean conditions are very calm, that's your best chance for seeing Harbor Porpoises. They're small enough that they don't rise very far above the surface, and they don't generate much of a "blow" when they breathe. So when the ocean is flat, use binoculars to watch for their small arching backs and triangular dorsal fins. (I posted a few photos of them in Washington last spring.)
For more information about Harbor Porpoises, check out the OBIS-SEAMAP web page.