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Big Lost River below Mackay Reservoir

Highest listed crest 6.08 ftFlood stage 4.3 ft22 crests since 1921

The Big Lost River below Mackay Reservoir crested above flood stage 12 times among the 22 crests the National Weather Service lists from 1921 to 2020. The highest, 6.08 ft on June 6, 1986, was minor flooding, 1.78 feet above flood stage. 2 other gauges on the Big Lost River crested above flood stage within a week of it.

The gauge

Highest listed crest
6.08 ft
June 6, 1986; 2,990 cubic feet per second
Flood stage
4.3 ft
No major stage set
Crests at major
0
12 above flood stage
Most recent flood crest
May 27, 2018
4.95 ft, minor flooding
Location
Custer County
Idaho

Flood stages

The thresholds the National Weather Service uses for this gauge today, and how many listed crests reached each.

Flood categories, Big Lost River below Mackay Reservoir
Action stage3.84Jun 17, 2019The level at which the NWS or its partners begin to take action
Flood stage (minor)4.312May 27, 2018Minimal or no property damage, but possibly some public threat

Every listed crest

22 crests from 1921 to 2020. Filled: at or above flood stage. Hover a crest for its date and stage.

Listed crests at the Big Lost River below Mackay Reservoir, 1921 to 2020 234567ft Flood stage 4.3 ft Jun 10, 1921: 5.79 ft, minor flooding; 2,990 cubic feet per secondMay 26, 1958: 5.65 ft, minor flooding; 2,520 cubic feet per secondJun 14, 1965: 5.89 ft, minor flooding; 2,640 cubic feet per secondJun 17, 1974: 5.93 ft, minor flooding; 2,790 cubic feet per secondJun 30, 1982: 5.65 ft, minor flooding; 2,490 cubic feet per secondJun 6, 1986: 6.08 ft, minor flooding; 2,990 cubic feet per secondMay 30, 2005: 4.07 ft, action stage; 1,350 cubic feet per secondJun 9, 2006: 5.52 ft, minor flooding; 2,580 cubic feet per secondMay 15, 2007: 2.87 ft, below flood stage; 591 cubic feet per secondJun 24, 2008: 3.29 ft, below flood stage; 829 cubic feet per secondJun 21, 2009: 4.64 ft, minor flooding; 1,800 cubic feet per secondJun 28, 2010: 4.44 ft, minor flooding; 1,690 cubic feet per secondJun 30, 2011: 4.77 ft, minor flooding; 1,910 cubic feet per secondJun 5, 2012: 4.05 ft, action stage; 1,340 cubic feet per secondJun 11, 2013: 3.30 ft, below flood stage; 811 cubic feet per secondJun 6, 2014: 3.12 ft, below flood stage; 732 cubic feet per secondJun 10, 2015: 3.15 ft, below flood stage; 752 cubic feet per secondJun 9, 2016: 3.91 ft, action stage; 1,280 cubic feet per secondJun 10, 2017: 5.09 ft, minor flooding; 2,280 cubic feet per secondMay 27, 2018: 4.95 ft, minor flooding; 2,150 cubic feet per secondJun 17, 2019: 4.19 ft, action stage; 1,530 cubic feet per secondJun 7, 2020: 2.78 ft, below flood stage; 561 cubic feet per second Highest, 6.08 ft, Jun 6, 1986 19401960198020002020

Crests at or above flood stage, by decade

Crests at or above flood stage per decade, Big Lost River below Mackay Reservoir 1920s: 1 1930s: 0 1940s: 0 1950s: 1 1960s: 1 1970s: 1 1980s: 2 1990s: 0 2000s: 2 2010s: 4 4 2020s: 0 1920s1930s1940s1950s1960s1970s1980s1990s2000s2010s2020s
  1. These are the crests the local National Weather Service office lists for the gauge: the highest on record and recent crests. Lesser floods between them may be missing, so counts by decade are a floor.
  2. Categories use today's flood stages. Levees, dams and channel changes since a crest can make old and new stages not directly comparable.

Highest crests

Highest listed crests, Big Lost River below Mackay Reservoir
1Jun 6, 19866.08+1.78Minor2,990
2Jun 17, 19745.93+1.63Minor2,790
3Jun 14, 19655.89+1.59Minor2,640
4Jun 10, 19215.79+1.49Minor2,990
5May 26, 19585.65+1.35Minor2,520
6Jun 30, 19825.65+1.35Minor2,490
7Jun 9, 20065.52+1.22Minor2,580
8Jun 10, 20175.09+0.79Minor2,280
9May 27, 20184.95+0.65Minor2,150
10Jun 30, 20114.77+0.47Minor1,910
11Jun 21, 20094.64+0.34Minor1,800
12Jun 28, 20104.44+0.14Minor1,690
13Jun 17, 20194.19−0.11Action1,530
14May 30, 20054.07−0.23Action1,350
15Jun 5, 20124.05−0.25Action1,340
16Jun 9, 20163.91−0.39Action1,280
17Jun 11, 20133.30−1.00Below flood stage811
18Jun 24, 20083.29−1.01Below flood stage829
19Jun 10, 20153.15−1.15Below flood stage752
20Jun 6, 20143.12−1.18Below flood stage732
21May 15, 20072.87−1.43Below flood stage591
22Jun 7, 20202.78−1.52Below flood stage561

The worst floods along the Big Lost River

For this gauge's highest crests, the other gauges on the Big Lost River that crested above flood stage within a week.

June 6, 1986: 6.08 ft here, minor flooding

  • ArcoID · Jun 9, 1986 · 7.26 ft · Minor
  • Howell RanchID · Jun 4, 1986 · 5.48 ft · Minor

June 17, 1974: 5.93 ft here, minor flooding

  • ArcoID · Jun 23, 1974 · 6.61 ft · Minor
  • Howell RanchID · Jun 16, 1974 · 5.41 ft · Minor

June 14, 1965: 5.89 ft here, minor flooding

Gauges on the Big Lost River

In USGS station-number order, which runs downstream within a river basin.

Flood gauges on the Big Lost River
Howell RanchID4.16.02 ft, May 25, 19670
Mackay Reservoir this gaugeID4.36.08 ft, Jun 6, 19860
ArcoID6.57.68 ft, Jul 5, 19670

Other gauges in Custer County

Flood gauges in Custer County
Howell Ranch4.16.02 ft, May 25, 19670
Wild Horse5.16.41 ft, May 21, 20060
Bruno Ck6.26.53 ft, May 7, 20170
Yankee Fork9.510.64 ft, Jun 5, 20170
Stanley3.14.60 ft, May 29, 19130
Clayton11.012.25 ft, Jun 1, 20170

Custer County: every hazard · River floods across the country · Idaho

NOAA National Water Prediction Service, gauge MAKI1, retrieved October 30, 2026. Stages in feet on the gauge's own datum, not elevation. Crests are as the National Weather Service lists them; preliminary values may be revised.