The pair, who were first spotted in public last weekend grocery shopping in L.A., rounded up their dogs – Seyfried's Australian shepherd Finn and Hartnett's mixed-breed pup Iggy – for a fun day at the beach in Malibu on Tuesday.
With Hartnett, 33, standing close by, Seyfried, 26, laughed as she watched Finn run in and out of the water. Later, Hartnett played fetch with Iggy and Finn by tossing a tennis ball over the sand.
It's no secret that Seyfried feels extremely connected to her pooch, and she takes him nearly everywhere she goes. "I'm obsessed with my dog," she told PEOPLE. "He's become my son and my light source and kind of a savior to a lot of people, a lot of my friends."
Hartnett, too, seems to be very close to his dog. Iggy is often spotted with the actor out on the town or at the park.