Call it “Hawaii O-C.”

Rachel Bilson was spotted splashing around in a sexy one-piece bathing suit while vacationing in Hawaii on Monday.

Bilson seemed to be taking her snorkeling very seriously. MEGA

The “O.C.” actress, 39, showed off her curves in the plunging black-and-white cheetah-spotted swimsuit, a departure from her usual swimwear, at least judging from her tan lines.

She was also seen wearing flippers as her footwear of choice. MEGA

Bilson kept her beach look casual, with her hair in a high ponytail and her black shades on as she splashed about in the clear blue water and relaxed on the sandy beach.

She clearly had been spending a lot of time in the sun as she had major tan lines on her backside. MEGA

Later she was spotted sporting snorkeling gear, using goggles and flippers as she explored the shallows.

She seemed to be in good spirits, cracking the occasional smile, though she looked markedly determined at one point while adjusting her snorkeling mask.

And Bilson looks to have taken herself on her getaway, as she appeared to be hitting the sands solo.

She rocked her sunnies as she strutted her stuff along the beach. MEGA

She was most recently romantically linked to Bill Hader, but the pair broke things off after nearly seven months of dating in July 2020. They had made their red carpet debut in January last year at the 2020 Golden Globes after first sparking dating rumors that month, as we exclusively reported at the time.

Bilson was previously in a long-term relationship with Hayden Christensen but split up after nearly 10 years in 2017. They share a 6-year-old daughter, Briar.