What is CFS?
Wondering what CFS river flow means when you are booking a trip? CFS stands for “cubic feet per second,” which is a hydrological unit of measurement referring to the volume and speed of water flow. One cubic foot is roughly the size of a basketball. If a stream is flowing at 100 CFS, imagine 100 basketballs rolling down a riverbed together every single second.
Depending on the waterway’s descent, width, and arrangement of the rocks, a higher volume can usually mean you’ll encounter larger rapids. Gauges are installed on major rivers to measure this data, and that real-time information can easily be found online through city water data sites and the USGS.
Mastering the basics of CFS river flow is the first step to mapping out your day on the water. It is a common myth that a river’s volume dictates how difficult the rapids will be. In reality, river difficulty is measured by the International Scale of River Difficulty, which rates rapids from Class I to Class VI based on technical maneuvering, wave size, and inherent risks. While a high volume can certainly change the behavior of a rapid, the classes themselves are a measurement of technical difficulty, not water speed. For example, a massive river can feature a high CFS river flow while remaining a gentle, rolling float, while a narrow mountain creek can have a tiny volume but feature intense, steep drops. When you book a trip, our team matches you with the perfect rapid class for your comfort level, whether you want a relaxing float or an adrenaline-filled white water challenge.
The Secret to River Flow: It’s All Relative
To truly grasp how CFS river flow impacts your trip, you have to understand that the shape of the river canyon changes everything. The exact same number can create a completely different experience depending on where you are paddling. When a massive amount of water is forced through a tight, steep canyon, it creates fast, powerful, and continuous waves. However, if that same amount of water enters a wide, flat valley, it spreads out into a shallow and gentle current.
This relative nature of water volume means that the high water season, which typically peaks during the late spring snowmelt in May and June, brings fast-paced, roller coaster waves where rocks are deeply submerged. As the summer heat rolls into August, the volume naturally drops, exposing hidden boulders and creating a technical, splashy obstacle course that requires precise paddling and quick maneuvering.
Mild to Wild Rivers and Their Volume Ranges
Mild to Wild runs many rivers throughout Colorado, Utah, and Arizona. Our river permits include iconic Southwest destinations, each behaving uniquely according to its specific volume.
Colorado Rivers
- Lower Animas (Durango): The Lower Animas generally runs between 300 and 4500 CFS, providing a beautiful and fun-filled introduction to white water with plenty of Class I and II water. The main excitement happens right in the heart of Durango at the Smelter Rapid, also known as Santa Rita White Water Park, which serves up fun Class III splashes. During the peak of the spring runoff, the CFS river flow can surge past 3800, making the white water park a class IV rapid. When the river hits these high water levels, our experienced guides bypass the park entirely by launching our rafts at a secondary access point just downstream.
- Upper Animas (Durango): CFS range 500 to 3,000. The Upper Animas has three distinct white water sections, all of which come with at least Class III and IV rapids. The Silverton Section and Needleton Section are the rowdiest, with constant Class III rapids, alongside a few intense sections with Class IV and V drops. The Rockwood Section comes with technical Class II, III, and IV(+) water.
- San Miguel River (Telluride): CFS range 180 to 900. The San Miguel River offers constant Class II with intermittent Class III rapids, making for an exciting intermediate-level trip.
- Dolores River (Cortez): Running the Dolores River is a legendary bucket list experience because its flow relies entirely on a water release from the McPhee Reservoir. The river fluctuates wildly between 800 and 5000 CFS, making it an incredible privilege to catch when the gates open. When the CFS river flow hits that perfect sweet spot, it wakes up the ancient Ponderosa Gorge, churning out stunning Class II, III, and IV rapids surrounded by towering red rock walls. Because the water drops quickly once the release ends, timing is everything for this rare desert gem.
- Piedra River (Pagosa Springs): CFS range 400 to 3,000. The Upper Piedra has Class II, III, and IV white water with some short sections to rest, unlike the continuous nature of the Upper Animas. On the Lower Piedra, Class III, IV, and V rapids through staircase drops and chutes make this a highly technical and adventurous rafting experience. This section of the canyon is narrow, so if the water volume is too high, some rapids must be portaged.
- Yampa & Green Rivers (Dinosaur National Monument): CFS range 1,000 to 25,000. The confluence of the Yampa River and Green River resides in Echo Park, where the joining waterways make for incredibly fun Class II and III rapids in Whirlpool Canyon. Before joining the Green, the Yampa River can flow between 1,000 and 14,000 CFS with occasional Class II and III rapids, and one legendary Class IV called Warm Springs. The Green River in Lodore Canyon can flow between 1,500 and 5,000 CFS here, churning up incredible Class II and III rapids through Disaster Falls and Hell’s Half Mile.
- Clear Creek (Idaho Springs): CFS range 100 to 1,200. Clear Creek is a steep, narrow, and fast-moving waterway that provides a technical river experience. During peak runoff between 500 and 1200 CFS, the creek offers rolling waves, crashing holes, and consistent head-to-toe splashes.
- Arkansas River (Buena Vista): CFS range 300 to 4,500. Moderate flows between 650 and 2,000 CFS offer a textbook class III experience through Browns Canyon. In Early summer, peak flows exceeding 2,000 CFS push The Numbers and Royal Gorge into Class IV+ and -V territory.
- Upper Colorado River (Kremmling): CFS range 300 to 5,000. For a scenic escape, the Upper Colorado River features mild Class I and II ripples. The early summer melt brings a faster current and splashier waves. Because of its dam-regulated flow, it remains a premier destination into late summer and autumn.
Utah Rivers
- Green River (Desolation Canyon): CFS range 5,000 to 25,000. This 95-mile stretch of the Green River offers relatively friendly whitewater at most water levels. Desolation Canyon comes with more than 60 Class II & III rapids throughout its beautiful wilderness drift.
- Lower Colorado River (Castle Valley & Cataract Canyon): CFS range 3,000 – 60,000. The Castle Valley section of the Lower Colorado River near Moab ranges from 3,000 to 30,000 CFS. This river section is characterized by rolling Class II waves and Class I currents (great for swimming). 50 miles downstream, the river reaches the confluence with the Green River, doubling the volume between 6,000 and 60,000 CFS. Here, the river enters Cataract Canyon, pinched by steep canyon walls, the immense volume transforms into some of the biggest, most powerful Class III, IV, and V white water in the entire American West, offering an unforgettable adventure for thrill seekers.
Arizona Rivers
- Salt River (Phoenix Area): CFS range 500 to 3,000. The Salt River resides in an ancient drainage basin below the White Mountains. Flows here vary tremendously based on desert conditions. On day trips, paddlers can rejoice in constant Class II and III rapids, while multi-day expeditions get to experience Class II, III, and IV drops.
Ready to Experience the River for Yourself?
At the end of the day, you do not need a degree in hydrology to have an unforgettable time on the water. While tracking the CFS river flow is a great way to form expectations for the river experience, the most important element of any raft trip is the team navigating the boat. Take a look at our current trip offerings, find the rapid class that matches your group’s sense of adventure, and let us handle the numbers while you enjoy the ride!
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