Jump off of the trail briefly and walk towards the water, but be careful not to disturb any of the other hikers who may be camping in the campground near the water.
Walk out to the large granite slab (it's hard to miss) for a great view of the lake, and an excellent place to take off your hiking boots and dip your feet in the water, or jump in and swim around for a while, but be prepared for some pretty cold water.
Walk back to the trail and continue along the north side of the lake and climb up some switchbacks before meeting up with the earlier trail just before Lake Aloha.