Fewer ferry sailings than usual have been scheduled for the normally busy period around August 15, a public holiday in Greece.
A total of 117 ferries were due to leave Piraeus, Rafina and Lavrio, Athens?s three main ports, on August 13, 14, and 15.
Greece?s financially troubled coastal shipping firms have seen passenger traffic drop this summer.
According to the coast guard, up to August 12, roughly 408,500 passengers had boarded ships leaving Athens, in comparison with more than 487,000 who had sailed from the capital during the same period last year.
Traffic police also noted a drop in the number of cars being driven out of Athens in August, when most Greeks take their summer vacation.
On the Athens-Lamia highway, traffic was down between 40 and 50 percent on August 12 and 13 compared to last year.
On the Athens-Corinth national road, there were between 35 and 50 percent fewer cars.
The number of cars leaving Thessaloniki also dropped substantially.
On August 12, there was a drop of 3 percent but on August 13, it was down 17.2 percent, when 66,600 vehicles exited the northern port city.