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Rock River at Lake Koshkonong

Highest listed crest 15.13 ftFlood stage 10.0 ft37 crests since 1990

The Rock River at Lake Koshkonong crested at major flood stage 6 times among the 37 crests the National Weather Service lists from 1990 to 2026. The highest, 15.13 ft on June 21, 2008, was major flooding, 5.13 feet above flood stage. 10 other gauges on the Rock River crested above flood stage within a week of it, 4 at their own highest listed crest.

The gauge

Highest listed crest
15.13 ft
June 21, 2008
Flood stage
10.0 ft
Major flooding from 11.5 ft
Crests at major
6
11th of 143 gauges in Wisconsin
Most recent flood crest
April 24, 2026
11.42 ft, moderate flooding
Location
Jefferson County
Near Fort Atkinson (6.7 mi), Whitewater (10.6 mi), Janesville (12.5 mi)

Flood stages

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

Flood categories, Rock River at Lake Koshkonong
Action stage9.011May 6, 2017The level at which the NWS or its partners begin to take action
Flood stage (minor)10.08Jul 7, 2024Minimal or no property damage, but possibly some public threat
Moderate flood stage11.07Apr 24, 2026Some inundation of structures and roads near the stream
Major flood stage11.56Mar 25, 2019Extensive inundation of structures and roads

Every listed crest

37 crests from 1990 to 2026. Filled: at or above flood stage. Hover a crest for its date and stage.

Listed crests at the Rock River at Lake Koshkonong, 1990 to 2026 810121416ft Flood stage 10.0 ftMajor 11.5 ft Mar 23, 1990: 9.45 ft, action stageMar 31, 1991: 8.93 ft, below flood stageDec 14, 1991: 8.52 ft, below flood stageApr 25, 1993: 12.23 ft, major floodingMar 21, 1994: 9.19 ft, action stageAug 23, 1995: 8.10 ft, below flood stageMar 14, 1997: 9.02 ft, action stageApr 23, 1998: 9.77 ft, action stageApr 28, 1999: 9.73 ft, action stageJun 7, 2000: 11.02 ft, moderate floodingJun 5, 2004: 11.49 ft, moderate floodingApr 7, 2007: 10.58 ft, minor floodingAug 30, 2007: 10.46 ft, minor floodingApr 18, 2008: 11.65 ft, major floodingJun 21, 2008: 15.13 ft, major floodingMar 29, 2009: 11.37 ft, moderate floodingMay 2, 2009: 10.02 ft, minor floodingMar 20, 2010: 9.18 ft, action stageJun 30, 2010: 9.44 ft, action stageJul 31, 2010: 11.17 ft, moderate floodingMar 30, 2011: 10.09 ft, minor floodingApr 22, 2013: 12.35 ft, major floodingJun 30, 2013: 10.02 ft, minor floodingMay 17, 2014: 9.71 ft, action stageJul 8, 2014: 9.68 ft, action stageApr 22, 2015: 8.69 ft, below flood stageDec 21, 2015: 8.76 ft, below flood stageApr 11, 2016: 9.43 ft, action stageMay 6, 2017: 9.78 ft, action stageMay 20, 2018: 10.33 ft, minor floodingSep 12, 2018: 11.62 ft, major floodingOct 15, 2018: 11.07 ft, moderate floodingMar 25, 2019: 11.50 ft, major floodingOct 15, 2019: 11.02 ft, moderate floodingJun 13, 2024: 10.01 ft, minor floodingJul 7, 2024: 10.10 ft, minor floodingApr 24, 2026: 11.42 ft, moderate flooding Highest, 15.13 ft, Jun 21, 2008 1990200020102020

Crests at or above flood stage, by decade

Crests at or above flood stage per decade, Rock River at Lake Koshkonong 1990s: 1 2000s: 8 2010s: 9 9 2020s: 3 1990s2000s2010s2020s
  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, Rock River at Lake Koshkonong
1Jun 21, 200815.13+5.13Major—
2Apr 22, 201312.35+2.35Major—
3Apr 25, 199312.23+2.23Major—
4Apr 18, 200811.65+1.65Major—
5Sep 12, 201811.62+1.62Major—
6Mar 25, 201911.50+1.50Major—
7Jun 5, 200411.49+1.49Moderate—
8Apr 24, 202611.42+1.42Moderate—
9Mar 29, 200911.37+1.37Moderate—
10Jul 31, 201011.17+1.17Moderate—
11Oct 15, 201811.07+1.07Moderate—
12Jun 7, 200011.02+1.02Moderate—
13Oct 15, 201911.02+1.02Moderate—
14Apr 7, 200710.58+0.58Minor—
15Aug 30, 200710.46+0.46Minor—
16May 20, 201810.33+0.33Minor—
17Jul 7, 202410.10+0.10Minor—
18Mar 30, 201110.09+0.09Minor—
19May 2, 200910.02+0.02Minor—
20Jun 30, 201310.02+0.02Minor—
21Jun 13, 202410.01+0.01Minor—
22May 6, 20179.78−0.22Action—
23Apr 23, 19989.77−0.23Action—
24Apr 28, 19999.73−0.27Action—
25May 17, 20149.71−0.29Action—
26Jul 8, 20149.68−0.32Action—
27Mar 23, 19909.45−0.55Action—
28Jun 30, 20109.44−0.56Action—
29Apr 11, 20169.43−0.57Action—
30Mar 21, 19949.19−0.81Action—
31Mar 20, 20109.18−0.82Action—
32Mar 14, 19979.02−0.98Action—
33Mar 31, 19918.93−1.07Below flood stage—
34Dec 21, 20158.76−1.24Below flood stage—
35Apr 22, 20158.69−1.31Below flood stage—
36Dec 14, 19918.52−1.48Below flood stage—
37Aug 23, 19958.10−1.90Below flood stage—

The worst floods along the Rock River

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

June 21, 2008: 15.13 ft here, major flooding

  • Fort AtkinsonWI · Jun 15, 2008 · 20.90 ft · Major · its highest
  • JoslinIL · Jun 21, 2008 · 16.61 ft · Major
  • JeffersonWI · Jun 19, 2008 · 15.64 ft · Major · its highest
  • MolineIL · Jun 17, 2008 · 14.91 ft · Major
  • RocktonIL · Jun 17, 2008 · 14.72 ft · Major
  • Latham ParkIL · Jun 18, 2008 · 14.30 ft · Major
  • Lebanon-3 E-Hwy MM bridgeWI · Jun 15, 2008 · 14.01 ft · Major · its highest
  • AftonWI · Jun 21, 2008 · 13.51 ft · Major · its highest
  • ByronIL · Jun 15, 2008 · 14.81 ft · Moderate
  • Rockford (Auburn Street)IL · Jun 21, 2008 · 7.39 ft · Minor

April 22, 2013: 12.35 ft here, major flooding

  • JoslinIL · Apr 21, 2013 · 19.11 ft · Major
  • Fort AtkinsonWI · Apr 22, 2013 · 18.12 ft · Major
  • ByronIL · Apr 20, 2013 · 17.08 ft · Major
  • MolineIL · Apr 22, 2013 · 16.53 ft · Major · its highest
  • NewvilleWI · Apr 23, 2013 · 8.51 ft · Major · its highest
  • DixonIL · Apr 20, 2013 · 18.16 ft · Moderate
  • RocktonIL · Apr 21, 2013 · 13.46 ft · Moderate
  • Latham ParkIL · Apr 22, 2013 · 12.82 ft · Moderate
  • Lebanon-3 E-Hwy MM bridgeWI · Apr 21, 2013 · 12.54 ft · Moderate
  • JeffersonWI · Apr 20, 2013 · 12.31 ft · Moderate

April 25, 1993: 12.23 ft here, major flooding

  • RocktonIL · Apr 21, 1993 · 12.84 ft · Moderate
  • JeffersonWI · Apr 22, 1993 · 12.29 ft · Moderate
  • AftonWI · Apr 23, 1993 · 11.41 ft · Moderate
  • WatertownWI · Apr 20, 1993 · 6.03 ft · Moderate

Gauges on the Rock River

Flood gauges sharing the river's name, linked within 80 miles of one another.

Flood gauges on the Rock River
AftonWI9.013.51 ft, Jun 21, 20083
ByronIL13.017.80 ft, Apr 20, 19735
ComoIL12.515.64 ft, Jul 23, 20170
DixonIL16.020.50 ft, Apr 20, 19731
Fort AtkinsonWI16.020.90 ft, Jun 15, 20082
JeffersonWI10.015.64 ft, Jun 19, 20081
Lake Koshkonong this gaugeWI10.015.13 ft, Jun 21, 20086
Latham ParkIL9.014.70 ft, Mar 26, 19753
Lebanon-3 E-Hwy MM bridgeWI10.014.01 ft, Jun 15, 20081
MolineIL12.016.53 ft, Apr 22, 201334
NewvilleWI6.58.51 ft, Apr 23, 20131
Rockford (Auburn Street)IL6.010.00 ft, Apr 20, 18811
Rockford (Fordam Dam)IL4.06.50 ft, Apr 20, 18811
RocktonIL10.015.54 ft, Mar 25, 19754
WatertownWI5.57.81 ft, Jun 13, 20082
JoslinIL12.019.24 ft, Jun 7, 200224

Other gauges in Jefferson County

Flood gauges in Jefferson County
Rome4.05.07 ft, Jan 19, 20220
Milford7.013.35 ft, Jun 16, 20083
Fort Atkinson16.020.90 ft, Jun 15, 20082
Jefferson10.015.64 ft, Jun 19, 20081
Watertown5.57.81 ft, Jun 13, 20082

Jefferson County: every hazard · River floods across the country · Wisconsin

NOAA National Water Prediction Service, gauge NVLW3, 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.