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.