Summer 2025 - Checking Stream Temperatures During a Heat Wave

These last couple of days have been warm ones and I was curious what was happening at the Jersey Valley Lake. Since Highway P is the scenic route back to La Crosse from there, I did a little stream temperature monitoring. We - Coulee Region Trout Unlimited, the Wisconsin Department of Natural Resources, and our research lab - have two dozen temperature loggers out in the Coon Creek watershed and probably about 30 in the Kickapoo River watershed for our lab's sculpin project. Today was about getting out of the house for a bit before the big heat hit and seeing what streams were doing. Today is expected to get a little warmer than yesterday. I got out before it got too warm - but it was still in the high 80's when I stopped for a late breakfast.

This post is a quick hitter - a way to share what is going on with stream temperatures. One significant note before you read on, I did this before the heat of the day today.

West Fork Watershed

These are the air (red) and water (blue) temperatures of the past 2 days at the stream monitor at the West Fork Sports Club in Avalanche. Yesterday's temperature peaked at a bit over 95F and the water temperature hit about 81.5F, which I probably don't need to tell you, is NOT conducive to trout. But that is nothing new on the West Fork.

The Jersey Valley "Lake" - an impoundment on the headwaters of the West Fork of the Kickapoo River, Vernon County.

First stop was Jersey Valley County Park to see what the "lake" looked like. I suspect that the lake is the largest - but certainly not the only - thing causing thermal issues on the West Fork of the Kickapoo River. Under the best of conditions, small dams on headwaters are not great for downstream temperatures. The current state of affairs - and by "current", I mean the past nearly 7 years since the 2018 floods - is not the best of conditions. The lake is not drained down to just a stream (as it is supposed to be) and the shallow "lake" behind the patched up dam warms significantly, causing issues downstream. How much this is responsible for warming downstream, there is little way to know for certain. However, it is a huge issue, probably the most significant single issue in the watershed.

If you can't read it - it says 79.3 degrees - this was the water temperature of the "lake" at 9:22 this morning.

The stream monitor at the West Fork told me that the stream down there was a bit over 72F. The surface of the lake was at 79.3F, about 12 degrees warmer than I measured when I took Peaceful Valley Road up to the West Fork above the "lake". The WDNR found a similar about 12 degree difference from above the lake and downstream of the lake last year when they had temperature loggers deployed.

Coon Creek Watershed

On the way home, I took a drive along Timber Coulee / Coon Creek on Highway P to Coon Valley. I'll present a photo journey - not to hotspot - but it might help anglers be a little more informed about how temperatures change along the river continuum.

57.6 - the coldest reading of the morning - at the Westby Rod and Gun Club on Timber Coulee.

Continuing downstream, Timber Coulee at Lars Hill Road was 63.1F - quite fishable. By the time I got down to Rullands Coulee, just above the Junction Pool (where it meets Timber Coulee), it was 69F and Timber Coulee was about the same. Berge Coulee came in cold - 63F - but it was not enough water to do much cooling of Timber Coulee which was 72F at the Olstad Road Bridge.

Timber Coulee just above Bohemian Valley at the Bob Jackson section.

At the Bob Jackson section, Timber Coulee was 74.3F and Bohemian Valley Creek was 71.1 - both too warm to fish. I did not drive up Bohemian Valley but I do have a temperature logger upstream so we'll see those data later this year. A bit downstream at the Highway P bridge, Coon Creek was an unfishable 73.9F. Then I took a drive along Spring Coulee Creek.

Spring Coulee at the upstream access would have been fishable at 65.7F.

Spring Coulee did exactly what was expected - it warmed up from fishable in the headwaters, to marginal in the upper-middle (Moilien Hill Road) was 68.7F, it was 72.3 at the Spring Coulee Road bridge, and 73.9F at the Neprud Property before reaching Coon Creek. Coon Creek below Spring Coulee was 75.9.

The last stop - Coon Creek at Coon Valley Memorial Park - was 75.4.

The last stop - other than The Stockyard for breakfast - was the park in Coon Valley where we (Coulee Region Trout Unlimited) hosted Coon Creek Trout Fest yesterday (June 21st).

Stocking Rainbow Trout into Coon Creek for Trout Fest.

A little air conditioning, some ice water, and a hearty breakfast. The last stop of the morning.

My Final Thoughts...

I saw about what I expected - there was not a ton of fishable water, but there was some. There is no better tool than a thermometer and some common sense to help you find fishable water, if you're so inclined to fish on days like today. I was not so inclined today, and saw few that were. I only saw two cars all day - both were in places that were above 70F when I saw them. Want to find fishable water? Head upstream, find places with shade. Or go hit the Mississippi River.

Jersey Valley Lake in its current state.

I write about stream temperatures a lot, I know. But for trout, there is no more critical issue than temperature. This recent heat spell was a rather significant one. As important as the 90-plus degree highs was the fact that air temperatures were in the low-80's and high 70's overnight (overnight low was 76.4F). When we get cooler nights, streams cool off more significantly - as seen in the figure below from the West Fork Sports Club's stream monitor.

The past week's air (red) and water (blue) temperatures.

Quite honestly, more anglers need to be aware of stream temperatures. First, you are not going to have a very good day on a warm stream. Fish are not going to eat when they are stressed. Second, if you do hook into trout, their chances of survival go down quite drastically above 68F but particularly just a couple of degrees above that. Lastly, you are unnecessarily making trout move as you wade through them at a time they want to hunker-down and ride it out. Carry a thermometer - it is so easy and cheap and will save you some awful fishing - if you're so inclined to fish on days like today.

A recent electrofishing sample on Coon Creek where we captured a few hundred trout.

These are the days that really stress trout. However, as evidenced by recent electrofishing surveys I've been part of, these streams are full of trout - at least in the Coon Creek watershed. Things on the West Fork are not so rosy, and the fishery has been on the decline since the 2018 floods.

Some data from CRTU and UW La Crosse temperature loggers from 2024. These are the % of July observations where water temperatures were above 70F.

Last summer was a little wetter at this point, and we'll see how stream temperatures compare. The figure above gives some pretty good insights. There are many streams where temperatures are rarely too warm, but others where it is pretty common. This is my personal opinion, but small dams on trout streams do them no favors. Their fake lakes, err reservoirs, are not deep enough for bottom draws to have the effects that they do for tailwater rivers. The two streams that stick out here - the West Fork of the Kickapoo and the North Fork of the Bad Axe - are both below small, county-owned impoundments. Runge Hollow Dam is not the Navajo Dam on the San Juan River, and Jersey Valley is not Flaming Gorge Reservoir.

We have two dozen loggers in the Coon Creek watershed and about 30 in the Kickapoo River watershed. We'll have yet more data to share after this summer and a better understanding of stream temperatures in two important Driftless Area watersheds. More on temperatures to come, to be sure.

I put this together quickly - let me know of any errors you find...