Rivermatics

4 USGS Streamgages · Mississippi River system

Sun River flows and levels

Sun River is gauged at 4 USGS streamgages in Montana, each tracked by Rivermatics. The mainstem runs about 129 miles (208 km) from headwaters to outlet. It drains into the Mississippi River system. Drainage area at the gauges ranges from 610 square miles at Sun River below Diversion Dam near Augusta, MT up to 1,774 at Sun River near Vaughn, MT. The gauged reach falls about 1,037 feet, from 4,377 feet down to 3,339. Rivermatics issues a daily machine-learned 14-day flow outlook for every one of them.

Gauges on this river, upstream to downstream

Ordered by drainage area, which is how far down the river each gauge sits. April and July figures are long-term median daily flows for that month from the USGS record — historical normals, not a forecast and not today's reading.

USGS streamgages on this river, ordered upstream to downstream
Gauge State Drainage sq mi Elevation ft April p50 cfs July p50 cfs Forecast
Sun River below Diversion Dam near Augusta, MT MT 610 4,377 165.8 161.7 14-day
Sun River below Willow Creek near Augusta, MT MT 814 3,967 183.7 248.3 14-day
Sun River at Simms, MT MT 1,296 3,555 209.9 141.8 14-day + temp
Sun River near Vaughn, MT MT 1,774 3,339 293.8 558.9 14-day

Typical flow by month at Sun River near Vaughn, MT

The furthest-downstream gauge on this river, so the fullest flow it carries here. Long-term daily discharge percentiles from the USGS record (up to 92 years of data), averaged within each month. These describe the historical normal range — they are not a forecast and not today's reading.

Historical monthly discharge percentiles in cubic feet per second
Month Low p10 Typical p50 High p90 Range
January 137.3 245.3 400.8
February 148.3 247.1 423.9
March 164.5 266 544.9
April 145.8 293.8 1,025.5
May 221.8 1,131.9 3,435.2
June 400.9 1,696.3 5,174
July 323.2 558.9 1,536.6
August 303.7 536.4 788.9
September 227.6 425.9 635.4
October 231.4 352.2 528.5
November 207 300.6 479.1
December 159.7 263.5 471.1

All values in cubic feet per second (cfs).

Common questions

When does the Sun River run highest?
June, on the long-term record at Sun River near Vaughn, MT — the furthest-downstream gauge Rivermatics tracks on this river. Median daily flow there is about 1,696.3 cfs that month, against 245.3 cfs in January, the lowest. Upstream gauges peak on their own schedule; the table on this page gives April and July for each.
How many gauges are on the Sun River?
Rivermatics tracks 4 USGS streamgages on the Sun River, across Montana. Each has its own page with the site's full flow record and monthly normals. The river may carry other gauges that publish neither daily values nor discharge statistics; those are not tracked here.
Is there a flow forecast for the Sun River?
Yes, at 4 of the 4 gauges. Rivermatics trains a machine-learned model — a temporal-fusion transformer — on each basin's observed flows, weather and snowpack, and issues a daily outlook reaching 14 days ahead: a median estimate inside a confidence band, not a single number to bet on. Every forecast is scored against days the model never trained on, and that track record is published on each gauge's live screen.
What river system is the Sun River part of?
The Sun River drains into the Mississippi River system — it is a tributary somewhere in that chain, following the flowpath down to its terminal river. Rivermatics builds this from the USGS/geoconnex reference-mainstem network rather than from names.
Can I use Sun River data for flood or safety decisions?
No. Rivermatics provides estimates, not guarantees, and the readings and forecasts here may be delayed, inaccurate, or wrong. Do not use them for navigation or for any safety, rescue, or emergency decision. Check the National Weather Service and USGS directly, and use your own judgment.

Other rivers in the Mississippi River system

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