Rio Grande, New Mexico The Lower Taos Box of the Rio Grande usually dries out by the end of June. This year, Santa Fe–based Kokopelli Rafting Adventures will likely run Class III–IV day trips through July, thanks to runoff from Colorado's Wolf Creek range (day trips from $100; kokopelliraft.com). Kayakers who want to take it up a notch can put in at Little Arsenic Trailhead and tackle the Class V Upper Box.

Lower Salmon River, Idaho The Garden Company's five-day, Class III Rite of Passage trip on the Lower Salmon threads the basalt canyons of Nez Percé country. This year, the river will benefit from a late-season combination of big rapids and clear water—perfect for swimming or kayak-surfing the standing waves around Riggins ($360; thegardencompany.com).

Forks of the Kern River, California Only three hours from Los Angeles, the Forks of the Kern offers one of California's most intense Class V commercial raft trips, and the cathedral-like geology of the Kern Canyon rivals any national park's (two-day trips from $725; whitewatervoyages.com).