Jake Paul‘s fiancée Jutta Leerdam made a splash in more ways than one at an indoor water park on Friday — turnin’ heads with her surfin’ skills … and teeny bikini!

The couple seemingly took a break from filming their new reality show, “Paul American” (we see no TV cameras in sight) … and hit up the DreamWorks Water Park in East Rutherford, NJ to catch some waves at Skudin Surf.

Leerdam — an Olympic speed skater — went solo, proudly filming his boo as she rode the waves, showcasing her incredible athleticism, and drop-dead gorgeous body!

The couple also rode some water rides together, sneaking in a smooch, as they hung with several friends.

Jake and Jutta have been smiling from ear to ear ever since their engagement … when 28-year-old Paul dropped to one knee and proposed to 26-year-old Leerdam in Saint Lucia.

The 11-1 boxer put a massive 12-carat diamond rock on Leerdam’s finger … as the silver medalist literally jumped for joy when she saw the ring.

The ring also features Jutta’s initials and birthstone … as well as an oval-cut diamond resembling the shape of an ice rink.