Small stream water temps

[sarce]

I used to think on small streams, water temp isn't really an issue. But in the past year or so and especially lately, I've had a few experiences that were pretty eye-opening.

I don't have a thermometer but Brownie101 does and we fish a lot of the same little brook and brown trout creeks in SE PA. This year on some of the brookie streams he was getting temps of 66-69 degrees in the afternoon in early summer. I knew just from experience that the catching on these creeks goes wayyy down by mid-to-late June and I don't fish for the brookies much once the streams get low. Until he took the temps I had not thought water temp was the cause, I thought it was just low, clear water turning them off.

We've had an exceptionally cool summer and about average rainfall here, but I think in hot summers, some of these brookie streams Brownie and I fish must easily hit 70 degrees in the afternoons consistently for a month or longer. Anyone happen to know what water temp native brookies can handle? I would like to get an idea of how concerned I should be about the water temps on these creeks.

Now for a little story from today. I decided to check out a tributary of one of the streams mentioned above. The main creek has all brook trout to my knowledge, no browns. So the tributary should have brookies (or at least a few brookie fingerlings) and be colder because it is smaller, right? That was my logic, but it turned out I was wrong.

The tributary was noticeably warmer than the main creek. The first few pools up from the mouth were all teeming with big creek chubs. I thought I was in for a disappointment until I came to a huge pool on the downstream side of a culvert. I could see more chubs cruising near the tailout, so I cast up above them to try to avoid them. As soon as the fly hit the water a dark shape rushed out from the bank and whacked the fly. Somehow, I missed the hookset but the fly was still in the water and this fish followed and stared at it right to my feet. The fish came to rest right in front of me and I could see clearly that it was a wild brown about 9" in length.

I found it really odd that this brown found its way into this tiny creek (I did not see any smaller trout to suggest much reproduction). But in a way, it made sense that where the water is too warm for brookies, the brown trout do just fine. Looking on a map, the headwaters run through people's front yards and an open meadow before reaching the woods where I was fishing...no wonder the water was warm.

I decided to go check out the main creek just upstream from the mouth of this tributary, a section that I had not fished before. I wondered if maybe browns had established themselves here too. Nope...I spooked one trout before hitting private property and it was a very nice sized brookie.

Conclusion: I should have bought a thermometer a while ago because even on small streams, water temp can play a big factor in the fishing experience.

Just some food for thought...would like to hear some thoughts from the other small stream guys.

 

[Chaz]

The scientific literature says 78 degrees, but having taken hundreds of stream temperatures over the years, I know they can survive short periods a bit higher.
I do know that at around 64 degrees the brookies seem to simply turn off. Especially when the nights are over 70 degrees it's important to carry a stream thermometer. Freestone streams very fairly get cooler than the night time air temperature unless there are big springs feeding them.

 

[evw659]

interesting observations sarce. I've noticed some of the same things on small streams, especially with browns turning up in unlikely places, and wondering how they got there. on one stream I've fished 3 or 4 times, I've caught all brookies, then one day i caught 2 wild tiger trout...go figure.
temps can become an issue on little freestones, but it varies significantly from stream to stream. the topography of the watershed plays an important role. if its in a shallow valley, the nighttime lows are usually similar to the surrounding areas, but in a steep hollow, cold air settles into the valley and keeps the nighttime lows much colder than surrounding areas, keeping the water temp cooler overall.
the gradient of the stream and amount of canopy in the headwaters is another important factor.
i think these two factors alone may play the biggest part in regulating temps in small streams, though there are other factors that can be important on some streams.
just some thoughts...

 

[troutbert]

Small streams can get pretty warm during low flows and hot air temp periods.

Many of you are familiar with Cross Fork Creek, which holds both wild brookies and browns.

It got up to 80F at the Hungry Hollow Road bridge during a drought.

 

[Brownie101]

Troutbert, I was actually on Cross Forks 2 weeks ago. The temp was 55. We were having a very cool week in the 50's though. I do believe it could reach 80.

I think the stream Sarce was on today had a water temp of 67 in early June. This was before the heat of the summer (which hasn't been bad this year) and flows were still good. Its "twin" stream down the road was similar temperature around the same time. It makes me wonder how warm it gets during a drought.

What I find really interesting, us how in most of the small streams we fish are all brookies, or all browns. In the one Sarce fished today, we never caught a brown out of. Strange how there was a brown in a Trib to it.

Edit: I also remember this year, fishing this stream with sarce upstream further, I took the temp of a small trickle that was 71 in very early June. Really weird.

 

[Fishidiot]

Always carry a thermometer when fishing and use it frequently.

I use mine a lot in the winter too.

 

[troutbert]

The main point that you are raising is that small streams can get quite warm, and that is very true.

And it's kind of disconcerting because we tend to think of small streams as adding cool water to the larger streams that they flow into, providing thermal refuge for the trout in those large streams in the summer.

But if the tributary gets quite warm itself, it's not going to be providing much thermal refuge to the big stream it flows into.

The bottom line of all this from a conservation and restoration perspective is the importance of restoring and maintaining normal riparian vegetation along the entire length of all the streams, no matter how small, in the watershed.

In the pre-disturbance landscape there were a lot of tall trees along the streams. If you really look at streams as you are out exploring, you'll notice how common it is to see stretches of stream where there are few to no trees. The trees have been removed, and the vegetation is currently managed as grass or some other type of low vegetation, that does not provide much shade.

This is true even in "Big Woods" country in NCPA, in watersheds that people tend to think of the streams as being "forested freestone streams."

If you step out of that preconceived notion of what the streams are like, and look at what is really there, you'll see how very common it is for long stretches to have their trees gone. Or the trees are coming back, but still are very small.

In many places a road is right along the creek, and on that side there are no trees shading the stream.

And in many places the trees along the creek were cleared long ago, i.e. somewhere around 1880 - 1920. And have been maintained as cleared land ever since.

Many people who have properties adjoining the streams maintain the riparian vegetation as mowed grass.

Also, there are many impoundments on small streams that greatly warm the water. Some of these are private, and some are owned and maintained by the state.

 

[PatrickC]

I read something the other day (it slips me where it was) that we need to reconsider how we look at the size of riparian zones. We see these numbers in discussing management of riparian zones in terms of stream width. So for instance a stream that is 2 meters wide needs a healthy riparian zone of 20 meters. This person suggested a mile and half is what we really need to be considering. Now, that is about impossible in many areas, but it does make you stop and think about the impact we have on streams. In reality, a mile and half probably isn't enough (for many rivers) when you consider how drainages work. Well anyway, food for thought when you are wondering if or what kind of an impact you have on a stream. It's probably even greater than we realize.

 

[geebee]

a thermometer will also help you find cool springs on a warming creek.

i always always carry a thermometer - i wish more of the USGS sites had water temps too.

talking of water temps - manada creek was 10C yesterday and 8C today. i've not fished it, but i can't find any mentions of it being a spring limestoner or a tailwater ?

 

[sarce]

Chaz wrote:

The scientific literature says 78 degrees, but having taken hundreds of stream temperatures over the years, I know they can survive short periods a bit higher.
I do know that at around 64 degrees the brookies seem to simply turn off. Especially when the nights are over 70 degrees it's important to carry a stream thermometer. Freestone streams very fairly get cooler than the night time air temperature unless there are big springs feeding them.

Thanks Chaz. That upper limit is a bit higher than I expected. Brookies turning off around 64 degrees matches up well with what Brownie and I have observed. Foxgap and I fished one of these creeks this week and failed to land any brook trout over 4" long. This is a creek where double digit days can happen in April and May and none of the fish will be under 6". In one pool we watched several of them completely ignore our flies. Water temp was 66...

Brownie101 wrote:

I also remember this year, fishing this stream with sarce upstream further, I took the temp of a small trickle that was 71 in very early June. Really weird.

Remember the trickle running into the other branch of the creek that was 75? Air temp was only around 80 I think.

Troutbert wrote:

The main point that you are raising is that small streams can get quite warm, and that is very true.

And it's kind of disconcerting because we tend to think of small streams as adding cool water to the larger streams that they flow into, providing thermal refuge for the trout in those large streams in the summer.

But if the tributary gets quite warm itself, it's not going to be providing much thermal refuge to the big stream it flows into.

The bottom line of all this from a conservation and restoration perspective is the importance of restoring and maintaining normal riparian vegetation along the entire length of all the streams, no matter how small, in the watershed.

Agree 100%. But if brookies can tolerate upper 70s, I probably don't need to worry too much about these creeks. I am concerned about runoff from hot pavement after summer storms. I am sure the temp probably spikes close to 80 during those events.

PatrickC wrote:

This person suggested a mile and half is what we really need to be considering. Now, that is about impossible in many areas, but it does make you stop and think about the impact we have on streams.

It depends what you are trying to accomplish I guess...just make a stream livable for trout, or restore it to pre-development quality? We see many places where trout survive just fine without a mile and a half buffer zone. It does make you think though.

 

[salmonoid]

troutbert wrote:
The main point that you are raising is that small streams can get quite warm, and that is very true.

And it's kind of disconcerting because we tend to think of small streams as adding cool water to the larger streams that they flow into, providing thermal refuge for the trout in those large streams in the summer.

But if the tributary gets quite warm itself, it's not going to be providing much thermal refuge to the big stream it flows into.

The bottom line of all this from a conservation and restoration perspective is the importance of restoring and maintaining normal riparian vegetation along the entire length of all the streams, no matter how small, in the watershed.

In the pre-disturbance landscape there were a lot of tall trees along the streams. If you really look at streams as you are out exploring, you'll notice how common it is to see stretches of stream where there are few to no trees. The trees have been removed, and the vegetation is currently managed as grass or some other type of low vegetation, that does not provide much shade.

This is true even in "Big Woods" country in NCPA, in watersheds that people tend to think of the streams as being "forested freestone streams."

If you step out of that preconceived notion of what the streams are like, and look at what is really there, you'll see how very common it is for long stretches to have their trees gone. Or the trees are coming back, but still are very small.

In many places a road is right along the creek, and on that side there are no trees shading the stream.

And in many places the trees along the creek were cleared long ago, i.e. somewhere around 1880 - 1920. And have been maintained as cleared land ever since.

Many people who have properties adjoining the streams maintain the riparian vegetation as mowed grass.

Also, there are many impoundments on small streams that greatly warm the water. Some of these are private, and some are owned and maintained by the state.

Even in areas that have been cleared long ago, some of them have never fully recovered, even though the last real disturbance was over a hundred years ago. Some streams that I consider to be really good would be truly great if those large trees would ever grow back. But the floodplain is now just grasses, blackberries and scrub. And while they still run cool enough through the summer, they would run cooler still and they would have a larger chilling effect on thermally impacted streams downstream. Nature does reclaim its own, but its a very long time to fully eradicate the imprints of humans.

A thermometer is definitely helpful to get a sense of the water temperature in a stream, but it still only provides a snapshot of the area of measurement. Further upstream or downstream, the temp may rise or fall significantly. Without a thermometer, you can still get a general sense of where the cooler water is. I used to be puzzled by the congregation of trout in seemingly obscure pools in certain streams. I thought I had hit a jackpot, but especially in warmer weather, they wouldn't turn an eye to a dry floated by. I've since figured out that I was really looking at a thermal refuge. One particular spot is very interesting to observe. Here are two photos that show the fish in their summer schools. Although the slight ripple on the surface makes details a bit fuzzy, there are easily 50 fish represented between the two photos.





The first photo is about ten yards downstream from a small tributary. The tributary will at times dry up on the surface over the summer. But there are always dozens of fish stacked up in the hole. The second photo is another ten yards below the first, so about twenty yards below where the trib enters. And it also always has fish stacked in it. So it's clear to me that there is some significant underground flow entering at both spots. These photos are from this year, so the fish seek these areas out, even when the summer is cooler. And the primary difference is this year, the fish were interested in feeding when presented with something that imitated food.

One other temperature contrast that I can clearly remember is fishing Little Kettle about ten years ago in late August. I was wet wading and it felt cold enough. There were a few fish I managed to pick up and I was working my way downstream from the Kettle Creek Lodge. About fifty yards from Kettle Creek, there was a fairly large spot of dead water and as I waded through it, I could sense the water temperature rising. But when I got to Kettle and stepped into the main flow of that stream, it was like stepping into bathwater. The stream must have been over 80 degrees. Naturally, the fishing died completely. I then fished upstream on Kettle and observed schooling of fish on what were probably springs, but at the time, was puzzled why they wouldn't hit anything. Only when we reached Long Run and fished up that did we pick up fish again.

 

[Swattie87]

geebee - Manada is a freestoner. I've taken temps on it at 70 deg F in recent Summers in the DHALO. Haven't been there this Summer but I'm sure it's running cooler this year given the relatively cool Summer.

 

[geebee]

thanks swattie - you'd think there must be cool tribs or springs.

Salmonoid - great stuff. that confirms much of what i've suspected. i've seen brookies shoal up like that too. they wouldnt hit a thing. i figured it was stress.

in CT on their streams they put wooden lattice structures in those spring 'holes; to protect the fish shoals being wiped out by Herons n cormorants.

it might be a good suggestion to the local TU - the CT TU has also made them downstream of all cold tribs.

the Project is only about 4-5 years old but they are already seeing a higher % wild to stocked browns.

 

[barbless]

When I see brook trout bunched up in small spring holes in the summer, it's practically like they're in aestivation (the summer equivalent of hibernation.) Practically all they're doing is breathing. They might get out at night to eat, I don't know. But it really seems like they're like bears in a den in wintertime.

 

[Mike]

"Farm ponds" and the like, particularly when they appear in a series on multiple riparian properties, may warm streams considerably with the cumulative effects of their individual discharges.

 

[wildtrout2]

All I can say is I fished 2 NC freestone streams yesterday, they were 25 miles apart, and they were both at 56F. That's cold for the middle of August, even for a mountain stream.

 

[troutbert]

If you check water temps on a stream when the nights are cool, and the day time air temps are modest, and the stream flows are up, you can't determine much about the water temperature "situation" on that stream.

Go there during a drought, when flows are low, when air temps are about 90F, with the sun beating down, and at around 4 pm, which about the time of day the water temps reach their max.

Check several streams, their tribs etc. in the same area, so you can compare.