Warm Water And Trout Survival

[ozark trout fisher]

I realize this isn't a really important issue in Ozark trout streams, where water temperatures are constantly cooled by springs or cold flows from dams, but it is sort of an interesting issue that came up on my trip to the Adirondacks this year.

On my trip, the weather was hot up there, and the river I spent the most time on (the West Branch of the Ausable) rose up to 78 degrees (that's the warmest I personally saw on my water thermometer, although someone told me they had seen it at 80 degrees). This seems like it would be lethal to the trout. But after a long stretch of these terribly hot water temperatures, there was a cold rain, and the water temperature dropped down into the upper 60s. And in the same stretch that had water temperatures that seemed like they should have been lethal just days before, the trout rose and I was able to catch some, including one of the incredibly temperature sensitive native brook trout. It was really a mystery to me how they survived. I didn't find any spring-holes or tributaries nearby, although they may have been there. The one possibility I did come across was the oxygenating effect of a mill dam a hundred yards or so upstream. Perhaps the white water coming over the dam had just enough oxygen in it to sustain the trout even though the water temperatures were too high. And maybe the white water from the many in-stream boulders helped to oxygenate the water as well. What do you all think?

[eric1978]

My opinion is purely non-expert, but I would say that yes, the mill dam would help tremendously. Also you mentioned the brook trout were native to that stream, so there may be some adaptation factor going on. That of course wouldn't apply to the browns and rainbows unless they were multi-generational at least.

I've heard stories about trout surviving the summers in some of the ponds at Busch. I'm sure that water easily reaches 80 degrees, possibly somewhat cooler in the depths, but there is no additional oxygenation happening there.

[Al Agnew]

Hmm...the mill dam might oxygenate the water below, but the mill pond above would probably make the water temps below go up even more than they would otherwise. Water probably coming off the top of the mill pond would be very warm.

I think trout can adapt to short stretches of very warm temperatures if that's normal for the stream they are living in, but 80 degrees seems excessive. I know that out in Montana, the fish and game people put on "hoot owl regulations" when the water temps get to where they are consistently above 73 degrees...they close the stream to all fishing after 2 PM, when the water temps will be the highest of the day. There is often a temperature swing of 6-8 degrees from the low in very early morning to the high in mid-afternoon.

I was floating the John Day River in Oregon one time in mid-July. This river has a steelhead run each year, but it's a high desert river, and the air temps routinely reach 100 degrees in mid-summer, so the water temps will get up into the high 70s and low 80s. I came to a place where a small tributary creek comes into the canyon. There is a big rock-fall at the mouth of the creek, and the creek sinks into the loose rock before it gets to the river, coming out at the edge of the river from under the rocks. It's just like a small spring, much cooler than the river water after its trip through the rocks. There were several young steelhead, lying with their noses right in the little trickles of outflow, and unwilling to move even a foot because they'd leave that tiny thermal refuge. Most of the young steelhead had probably already made their way back down into the Columbia, but these few hold-outs were in big trouble.

The Firehole River in Yellowstone Park is full of hot springs, and in the autumn and spring (and probably all winter) it's full of trout. But it gets up into the mid-80s and even hotter in the summer due to all the hot springs and warm weather combined. The trout, rainbows and browns, have been in the river for well over 100 years, but their survival strategy is simply to totally vacate the river in the summer. Some go up into the lower ends of cold water tributaries, but others go downstream into the Madison, which is cooler due to the influx of the colder Gibbon River.

[ozark trout fisher]

Hmm...the mill dam might oxygenate the water below, but the mill pond above would probably make the water temps below go up even more than they would otherwise. Water probably coming off the top of the mill pond would be very warm.

I think trout can adapt to short stretches of very warm temperatures if that's normal for the stream they are living in, but 80 degrees seems excessive. I know that out in Montana, the fish and game people put on "hoot owl regulations" when the water temps get to where they are consistently above 73 degrees...they close the stream to all fishing after 2 PM, when the water temps will be the highest of the day. There is often a temperature swing of 6-8 degrees from the low in very early morning to the high in mid-afternoon.

I was floating the John Day River in Oregon one time in mid-July. This river has a steelhead run each year, but it's a high desert river, and the air temps routinely reach 100 degrees in mid-summer, so the water temps will get up into the high 70s and low 80s. I came to a place where a small tributary creek comes into the canyon. There is a big rock-fall at the mouth of the creek, and the creek sinks into the loose rock before it gets to the river, coming out at the edge of the river from under the rocks. It's just like a small spring, much cooler than the river water after its trip through the rocks. There were several young steelhead, lying with their noses right in the little trickles of outflow, and unwilling to move even a foot because they'd leave that tiny thermal refuge. Most of the young steelhead had probably already made their way back down into the Columbia, but these few hold-outs were in big trouble.

The Firehole River in Yellowstone Park is full of hot springs, and in the autumn and spring (and probably all winter) it's full of trout. But it gets up into the mid-80s and even hotter in the summer due to all the hot springs and warm weather combined. The trout, rainbows and browns, have been in the river for well over 100 years, but their survival strategy is simply to totally vacate the river in the summer. Some go up into the lower ends of cold water tributaries, but others go downstream into the Madison, which is cooler due to the influx of the colder Gibbon River.

The thing that made the survival of these trout even more exceptional is that these water temperatures are not at all a normal phenomenon on the West Branch, so the trout presumably are not specially adapted to cope with ridiculously high temps. Now it is an eastern freestone stream, so it can get a bit warm, but according to what I've been told and read, there are quite a few summers that go by when it never cracks the 70 degree mark. Most folks I talked to said these were the warmest water temperatures they had ever seen.

My guess is that they found some little spring seep or a tiny tributary coming down from the mountains, and pushed their noses up against it until the water temps came down and they could spread back out. It does show me that trout are a bit tougher than most of us give them credit for.

[Quillback]

Here in Bella Vista, the POA started stocking trout in Lake Brittany 3 winters ago, all rainbows, 5,000 annually, 1,000 per month for 5 months starting in November, initially it was thought it would be a winter only fishery with the surviving trout expected to die off in the summer. Brittany is a small lake, 100 acres maybe, but near the dam it get's about 60 feet deep. The first two summers, ,the trout did survive until the next year, but our last 2 summers have been relativeliy mild. A couple of days ago I was fishing Brittany for bass and noticed a trout struggling on top and after a few minutes it turned belly up, so I went over a netted it, a nice 14 " fish. About an hour later I saw another one do the same thing. I took a couple of pictures and emailed our lakes biologist, he was disappointed to hear this, but there's not much to be done about it. It is cool enough below the thermocline for trout, but just not enough oxygen. It could be that the fish that died had wandered out of the cool zone and could not get back to it before croaking, but with the forecast for the hot weather to continue the future looks grim for these trout. Which is a shame as the ones that made it through the summer were nice colorful fish that could reach the 16-18 inch range.