Take a short walk along the well maintained pathway overlooking the pools, or jump in for a swim if you wish. Be sure to obey the warnings. Sometimes flash rain showers up the mountain can produce violent and unexpected flood waters swamping the pools. Injuries (even fatalities) have resulted. The park has a series of early warning gadgets up stream to give adequate warning. In the unlikely event that they go off....OBEY THEM.
A GREAT hike which too many ignore is the 2 mile Pipiwai Trail. Access from the parking lot is easy. If you're up to hiking 2 miles in and out, it's well worth it. There's a very tall (184 ft) waterfall (Waimoku Falls) at the end; but the hike itself is the hit. Among other things, you pass through a super bamboo forest. Just listen as the wind plays its music thru the bamboo.
Google "oheo gulch" for more info and photos.