The North Fork is the highest-elevation commercially run river in California, and is also considered one of the most difficult runs in the state with thirteen rapids at Class IV or above. The best flows are typically limited to a six-week window in April and May. During the summer, flows are regulated by New Spicer Meadow Reservoir, which most often releases water at night to generate hydropower. The Forest Service recommends taking a guided trip "due to the demanding and technical nature of the river", although private trips are also permitted. The Goodwin to Knight's Ferry run, though at a gentler gradient than the North Fork, also offers Class IV-V rapids. Below Knights Ferry the Stanislaus becomes wider and smoother, with Class I-II rapids between there and Orange Blossom Park; further downstream many parts of the river are suitable for flat-water boating and swimming.