Maryland · Potomac, MD

Potomac River (Mather Gorge) float season

Gauge 01646500 on the Great Falls and Mather Gorge above Little Falls. Kayakers surf Mather Gorge's bedrock waves minutes from the Capital Beltway, with Great Falls thundering just upstream.

kayaksup Fullest: Feb–Apr Leanest: Aug–Oct
Potomac River (Mather Gorge) — typical flow through the year Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 3k 15k 30k 50k
median flow for the date middle half of years (25th–75th percentile) most years (10th–90th)

Right now at this gauge

loading CFS

Checking the live gauge…

Live reading from the USGS gauge page for Potomac River (Mather Gorge). Provisional data — subject to revision.

The year on this river

In a typical year at the Potomac gauge, the Potomac River (Mather Gorge) runs fullest Feb–Apr and leanest Aug–Oct. Where today's reading falls inside that rhythm matters more than the raw number — the same flow that feels thin in spring can be the summer norm. Half of all past March days at this gauge ran above 15,700 CFS; the September median is 2,295 CFS.

Median of daily flows in each month across this gauge's full record — half of past days ran above these figures, half below.
Month Typical flow (CFS)
January 9,260
February 11,900
March 15,700
April 14,300
May 11,200
June 5,880
July 3,610
August 2,810
September 2,295
October 2,510
November 3,645
December 7,390

Record context

This gauge has measured daily flow since 1930 — 96 years of record. The largest daily average ever logged here was 426,000 CFS, in March 1936. Rivers do that sometimes; it's why the safety panel above isn't decoration.

Planning dates? The trip-window checker shows what flows have historically looked like on any week you pick for this river, or see what a CFS actually looks like.

More Maryland float rivers

Common questions

When is the Potomac River (Mather Gorge) usually at its fullest?

At the Potomac gauge, the fullest stretch of a typical year is Feb–Apr, with the single highest monthly median in March (about 15,700 CFS). The leanest months are usually Aug–Oct.

What is a typical summer flow on the Potomac River (Mather Gorge)?

The July median at this gauge is about 3,610 CFS — half of past Julys ran higher, half lower. Late summer is this river's lean season, so expect readings to drift down as the season goes on.

Is the Potomac River (Mather Gorge) safe to float right now?

No flow number can answer that, and this site never labels a river safe. What the data can tell you is how today's reading compares with 96 years of this date's history — well above typical means pushier, colder, faster water. Pair that context with a PFD, a look at the river from the bank, and a call to a local outfitter before you commit.

Which USGS gauge does this page use?

USGS gauge 01646500 (POTOMAC RIVER NEAR WASH, DC LITTLE FALLS PUMP STA), chosen because it best represents the Great Falls and Mather Gorge above Little Falls. Daily records here reach back to 1930.

Data: USGS gauge 01646500, approved daily records 1930–2026, retrieved 2026-08-07. Live readings are provisional and subject to revision. U.S. Geological Survey data is public domain.