Kendall Jenner Whips Around on Jet Ski in Barely-There Bikini

Kendall Jenner's making it hard to keep up with her these days ... and, we mean that literally 'cause she was zooming around the water at a lake in a tiny bikini!

The star was spotted in Washington state earlier this week ... cutting up the bright blue water in a little brown bikini, which showed off a lot of her popular posterior.

Jenner's locked in here ... keeping her concentration while zooming around the lake on the stand-up jet ski -- no stunt shots of her grinning for the cams here.

KJ's got perfect balance here ... kneeling down at times and bending forward at others -- and, we're surprised no one crashed around her, since she usually draws every eye in the area.

It's some much-needed time off for the star ... who just recently graced the cover of Vogue with her longtime pal Gigi Hadid.

The two saddled up together for a Western-themed photo shoot ... jumping on horses in flowing dresses and bringing frontier style back to the forefront of the fashion world.