What Is a Good CFS for Fly Fishing?

The short answer: a "good" CFS for fly fishing is any reading close to that river's seasonal median for the current month. There is no single magic number that applies to every trout river — the Madison at 1,200 CFS fishes great, and the South Platte at 1,200 CFS is a dangerous flood.

Here's how to actually read it.

Step 1: Look up the seasonal median, not the raw number

USGS publishes a "median daily statistic" for every gauge — the historical middle value for each day of the year. That's your baseline. A river running near median is running normal for the season. Angler Tech shows the current CFS and the seasonal median side by side on every river so you don't have to hunt for it.

Step 2: Match the current reading to a band

• **Below 70% of median** — low water. Concentrate on deep pools, fish small (18–22), long leaders, lighter tippet. Trout are stacked and spooky.
• **70–130% of median** — prime. Fish the full column. Attractors, matching nymphs, dries during hatches.
• **130–200% of median** — pushy but fishable. Move flies to the banks and inside seams. Add weight; upsize a hook.
• **200%+ of median** — high water / runoff. Streamers on the softest inside edges. Nymph the walk-in-safety line only.

Step 3: Check water temperature at the same time

CFS without water temp is half a picture. Trout stop feeding aggressively above 68°F and slow way down below 40°F. A perfect flow with 72°F water still fishes poorly.

That's why every Angler Tech river page shows CFS, seasonal median, and water temp on the same screen — the three numbers together tell you whether it's worth going.