Probably gastritis, which is fairly common in all dogs. An irritation of the stomach lining, it causes repeated vomiting for period of a cople of days. Can be brought on by any number of things... rotten meat, eating their own feces and possibly an overdose of sea water, as you've suspected.
Vomiting can change color from clear to yellow-green and back to clear during the period. Dog will sometimes exhibit diarrehea as well, but not usually to the really runny episodes.
Be sure to provide plenty of fresh water, to help protect the dog from dehydration during the period. Dog's temperature would probably be normal... 101 to 102.5 degrees Fahrenheit (38.3 to 39.2 degrees Celcius)(we're in the U.S., btw).
Here, Mrs. C's small Zuchon recently went through the same type of episode and only help we provided was to semi-force feed some fresh water with a rubber syringe (dog hated that, of course, but made Mrs. C feel like we were doing something). We see the same thing from time to time in our working dogs.
Of course, monitor the dog, but this isn't uncommon... If he becomes very lethargic and the event continues beyond, say 3 days, take it to the vet...