On June 20, summer officially descended on Colorado. And with families gearing up to go rafting in the Centennial State, they’re finding loads of information on rivers, rapids, trips, water levels and difficulty ratings. So what’s the difference between beginner and intermediate? Class II and Class IV?

Rapids are traditionally rated on a subjective class system from Class I to Class VI. Depending on the class of rapids along a section of river, raft companies label that section beginner, intermediate or advanced. A river such as Idaho Springs’ Clear Creek offers beginner, intermediate and advanced paddling. Beginners run Class I-III rapids and intermediate trips run a different section of river with Class III-IV rapids.

To make things more confusing, rapids can change class as water levels rise and fall. What’s suitable for five-year-olds during low water may be too rough for them during higher water. Often, rafting companies change the minimum age depending on river flows.

So if you’re planning a summer vacation in the middle of ski season, how do you know when Colorado’s rivers will be running? Traditionally, flows peak in spring and begin falling by mid-summer. But Summit County’s Blue River is too low for rafts by mid-June. Your best bet when you have questions: call the rafting company. Outfitters are a great resource for information on Colorado’s rivers and they’ll be able to help answer specific questions. As for the cost of airfare to Colorado, you’re on your own.

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Class I – Easy. Moving water with small riffles and no significant obstacles or waves.  

Class II – Novice. Clear rapids with waves, small drops and wide channels. Occasional maneuvering may be required. 

Class III – Intermediate. Moderately difficult rapids with larger irregular waves and often, narrow channels. Complex maneuvering to avoid obstacles required.

Class IV – Advanced. Powerful rapids requiring precise maneuvering in fast, turbulent water. Complex channels with many significant obstacles to be avoided.

Class V – Expert. Extremely long, violent or obstructed rapids, often following each other almost without interruption. Drops may have large, unavoidable waves and holes or steep, congested chutes with difficult routes. Steep gradient.

Class VI – Unrunnable.