River words, in plain words

CFS — cubic feet per second#

How much water is passing the gauge each second. One cubic foot is about a basketball, so 2,000 cfs is two thousand basketballs going by every second — a brisk walk. 15,000 cfs is a freight train: the same river, several feet higher, pushing into the trees.

The raw number means nothing by itself — 2,000 cfs is bony on one river and flood stage on another. What matters is where today's number sits in the run's own range, which is why every run page paints the flow chart in zones instead of asking you to memorize numbers.

Gauge & gauge height#

The USGS measuring station the flow numbers come from. Some gauges sit miles from the run they describe — each run page tells you which gauge it reads and when that's a directional hint rather than gospel.

Gauge height (in feet) is the older convention — how deep the water is at the station. Locals often talk in feet (“it's running 7.2”); the site talks in cfs. Both describe the same water.

Prime range / runnable range#

The flow window where a run is at its best — enough water to float clean, not so much that it turns pushy. On Riverbeta this drives the GO / OK / NO badge and the colored zones on the flow chart. The ranges are community estimates, not agency numbers; the ⚑ flags tell you which ones still need a local's confirmation.

The class scale (I–VI)#

The whitewater difficulty scale. In plain words — Class I: moving water with riffles; you could swim it calmly. Class II: straightforward rapids with wide, obvious channels; an accidental swimmer usually self-rescues. Class III: real rapids — irregular waves, moves you must make, swims that get serious. This is where “intermediate” starts meaning something. Class IV: powerful and precise; scouting expected, rescue takes practiced skills, self-rescue is hard. Class V: expert water with real consequence. Class VI: exploratory — effectively unrunnable.

A “+” means the hard end of the grade (III+ is a III that will humble you). And the same rapid changes class with flow: a friendly II at 1,500 cfs can paddle like a III+ at 8,000. The class on the page describes normal flows; the live verdict on each run page adjusts for today's water.

Percentile for the date#

How today's flow compares to every recorded year on this date. 90th percentile means the river is higher today than in nine of ten past years — useful context the raw cfs number can't give you. You'll find it right under the big flow number on each run page.

On-water time#

Our rough estimate of how long the float takes — but it's a typical-flow number, not a fixed one. The same run is a different day at a different level: high water can shave hours off (you're moving with a faster current), and low water adds them back (more drifting, more bumping, more lining through shallow gardens).

Treat it as a planning anchor, not a schedule. When a run page carries a paddler's report with a time at a stated flow, trust that over the estimate — and if you've run it, the time and flow you saw is one of the most useful things you can add back.

Strainer / sweeper#

A fallen tree (or log jam, or root wad) in moving current. Water pours through the branches; a boat or a swimmer doesn't — the river pins you against it and keeps pushing, like a colander straining pasta. A sweeper is the same hazard still attached to the bank, sweeping low over the water. A river-wide strainer blocks the entire channel with no way around.

Strainers kill more paddlers on these rivers than any rapid, and they kill strong swimmers in slow, easy water — Class I current is plenty to hold a person under a log. They also move: spring runoff picks whole trees up and re-plants them somewhere new, which is why dated wood reports (the Wood watch block on run pages) matter more than anything written in a guidebook.

The protocol is boring and absolute: scout what you can't see past, and portage anything with wood in the channel — walking around is never the wrong call. If a swim ever takes you toward one and you cannot get away: swim aggressively at it and go up and over the top, kicking hard. Going under is how people stay under.

Wood#

Paddler shorthand for every tree-in-river hazard — strainers, sweepers, log jams, single submerged logs. “The run is woody” means current reports have trees in play. Wood moves every season and with every flood pulse, so treat any wood report older than a few weeks as history, not beta.

Pin / wrap#

A pin is a boat (or worse, a person) pushed onto an obstacle and held there by current. A wrap is a raft folded around a rock by the same force. The fix is mechanical — ropes, angles, patience — which is why groups carry a pin kit and why “pin potential” in a rapid description deserves your attention.

Foot entrapment#

Standing up in moving water and getting a foot caught between rocks — the current then pushes you over and holds you down. The rule: never stand up in current deeper than your knees. Swim or float on your back, feet up and pointed downstream, until you reach an eddy or water shallow enough to crawl out of.

Hole / hydraulic#

Water pouring over a rock or ledge and recirculating back on itself upstream. Small ones are playspots; big ones can hold a boat or a swimmer and recirculate them. “Sticky” or “keepy” in a description means a hole that doesn't want to let go.

Cold water#

Montana rivers are snowmelt — often in the 40s°F right when the rapids are biggest. Cold shock steals your breath in the first seconds of a swim, and cold hands stop working in minutes. It's why the gear checklist on every run page changes with the live water temperature, and why “dress for the swim, not the float” is the rule here.

Eddy / eddy out#

The calm pocket of slack (or upstream-flowing) water behind a rock or inside a bend — the river's parking spots. To eddy out is to pull into one: it's how you stop to rest, regroup, or scout before committing. “Few eddies” in a high-water description means few chances to stop, which is most of why high water is serious.

Ferry#

Crossing the river without being washed downstream — angle the boat upstream and let the current push you sideways. The basic move for getting where you want to be before a rapid wants you somewhere else.

Line#

The path you intend through a rapid — “the line is right of center, then drive left.” Run descriptions on this site describe lines at typical flows; today's water may move them.

Scout#

Stopping — from an eddy or the bank — to look at a rapid before running it. The standing rule on every run page: scout anything you can't read from the boat, and anything with a “portage / scout” note. Looking is free; the alternative sometimes isn't.

Portage#

Carrying around a rapid or hazard instead of running it. Zero shame — on wood-prone rivers it's routine, and every honest paddler has a portage story they're glad to tell.

Read-and-run#

Whitewater you can size up from the boat as you go, without stopping to scout — the channel and the moves are visible from upstream. Most of the water on this site is read-and-run at normal flows. The phrase is a description, not a promise: wood and high water turn read-and-run water into scout-first water.

Wave train#

A line of standing waves down the middle of a rapid — the roller-coaster part. Usually the fun, friendly feature; at high water the same train gets big enough to flip rafts and swamp open boats.

River-right / river-left#

Always from the perspective of facing downstream — the direction the water is going. “Portage on river-right” means the right bank as you float. It never flips, no matter which way you happen to be looking.

Put-in / take-out#

Where you start (put in) and where you get off the water (take out). On committing runs, knowing the take-out matters as much as knowing the rapids — some of the worst water on these rivers sits just downstream of a take-out you must not miss.

Shuttle#

The car logistics: leave a vehicle at the take-out, drive boats to the put-in, retrieve at day's end. Every run page computes the drive. Budget real time for it — shuttles run long exactly when daylight runs short.

PFD#

Personal flotation device — a life jacket cut for paddling. Worn, zipped, and snug on the water; it's also Montana law for kids under 12 in moving boats, and Wild & Scenic corridor rules require one per person. The whistle clipped to it is the universal “look at me now” signal.

Throw bag#

A bag of floating rescue rope you throw to a swimmer while standing somewhere stable. One per paddler, accessible — not buried under lunch. Knowing how to throw it (and swim to one) is a skills-class thing, and worth the class.

Pin kit#

The unpinning hardware — webbing, carabiners, pulleys, prusiks — that turns a wrapped raft from a lost boat into a half-hour problem. Split between boats so it can't be on the boat that's pinned.