Trout Water Temperature: The 68 °F Line, Limits and Summer Refuges

Free PDF · Water temperature chart Take this thermometer to the water.

One reading, and the 16-page chart shows which of 26 fish are spawning, feeding hard or slowing down; for bass, crappie, bluegill and walleye, where they sit and what to throw. Every number sourced.

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Trout feed best in water of 55–65 °F (13–18 °C), and the day to stop fishing for them begins at 68 °F (20 °C). Brook trout stress sooner, at 65 °F (18 °C), and brown trout hold on to 70 °F (21 °C). Lake trout want it colder than any of them, 42–52 °F (6–11 °C). The upper 70s kill.

A rainbow trout grows fastest at 63 °F (17 °C) and dies at 77–79 °F (25–26 °C). Fourteen degrees separate its best day from its last one, which is why trout anglers carry a thermometer.

What temperature does each trout need?

Each trout gets four numbers. Comfort is the feeding band, and spawn is the temperature that starts the spawn. Stress is where the fish must find colder water. The stop line is where a caught trout starts paying for the fight with its life.

Brook trout are the tightest: West Virginia DNR calls anything above 65 °F a stress factor. Brown trout are the toughest, with a growth ceiling of 66–70 °F (19–21 °C). That is why browns survive in rivers that lost their brookies. Lake trout die at 74 °F (23 °C), a temperature a bass finds pleasant.

The wider water temperature chart puts these five next to twenty other species, from walleye and crappie to catfish and bluegill.

Can trout survive in warm water?

Briefly, yes; for a season, no. The lethal readings sit in the upper 70s. Rainbows die at 77–79 °F, brook trout at about 77 °F (25 °C), browns at 79–81 °F (26–27 °C). A stocked pond that reads 78 °F (26 °C) in July has no trout left to protect. Between 68 and 77 °F a trout lives, but it stops growing and holds in whatever cold seam it can find.

The reason is arithmetic. A fish’s metabolism roughly doubles with every 18 °F (10 °C) of warming, and a 1999 study across 69 species found much the same rule. A trout at 68 °F needs about twice the oxygen it needed at 50 °F (10 °C), while warm water carries less of it.

Add a fight and the fish runs an oxygen debt it may not repay. It can swim off and die hours later under a cut bank. That is why the catch and release numbers turn on the thermometer as much as on the hook.

The EPA’s Region 10 guidance draws the same line for Pacific salmon and steelhead. Its warmest criterion, for migration corridors, is 68 °F (20 °C) as a seven-day average of daily highs. Rearing water gets 61–64 °F (16–18 °C), and spawning water 55 °F (13 °C), so incubating eggs sit at 43–50 °F (6–10 °C).

Why do anglers stop at 68 °F?

Montana Fish, Wildlife and Parks turns the line into law. Under its drought policy, a river whose daily high reaches 73 °F (23 °C) on three days running gets a “hoot-owl” restriction. Fishing then closes from 2 p.m. to midnight, and the cool hours when the owls still call stay open. The department’s bulletins add the reason: 77 °F (25 °C) can be lethal to trout.

Low flows and poor water quality trigger restrictions too, and a reach that cannot cool at night can close at all hours, as the Madison below Ennis Reservoir did on July 15, 2026. The list changes weekly through July and August, so check FWP’s closures page before any summer trip in the state.

The rest of the country runs on the honor system, and the 68 °F line is the system. It is not a legal limit. It is the point where a trout you release stops being a trout you will catch again.

How do you take a stream temperature that means something?

A number from the wrong place or the wrong hour is worse than no number.

• In the current, not at the edge. The margin where you wade in runs warmer than the run the trout hold in. Drop the thermometer in knee-deep moving water, at the depth of the fish, for a full minute.
• Mid-afternoon, not dawn. A stream peaks in mid-to-late afternoon and bottoms out just after sunrise, and a small, open, unshaded stream swings the most.
• Trend beats level. A river falling from 70 to 66 °F (21 to 19 °C) after a storm fishes. One climbing from 62 to 66 °F under a heat dome is about to close.
• Move the thermometer. A tributary mouth, a spring seep or a shaded canyon reach can read several degrees below the main river a hundred yards (90 m) away. That difference is where the trout are.

Where are stream trout as the water warms?

The table is for rainbow, brown and brook trout in a stream, from late winter to the summer stop line, with the reading taken in the current. Lake trout and steelhead keep their own numbers in the first table. The same reading means something else on the way down, which is why the falling table further on is a separate one.

Where do trout go in summer?

Trout do not tolerate heat; they leave it. Four places hold them when the main river reads 70 °F.

Tailwaters. A dam draws from the cold bottom of a stratified reservoir. Below Greers Ferry Dam, Arkansas Game and Fish notes, the tailwater stays fairly constant even through short hot or cold spells. The first miles below a deep-release dam stay cool all summer.

Springs. Groundwater comes out close to the region’s year-round average air temperature, far below a July afternoon. A seep the size of a bathtub can hold a pod of brook trout through August.

Tributary mouths. A small, shaded, fast tributary runs colder than the river it feeds. Trout stack in the plume where the two meet, often within a rod length of the seam.

Depth, in lakes. From late June a lake stratifies and trout live under the thermocline, the layer where the temperature falls fast with depth. New York DEC’s trolling table gives lake trout 42–52 °F (6–11 °C), browns 54–63 °F (12–17 °C) and rainbows 55–65 °F (13–18 °C), close to the chart’s comfort column; its steelhead figure is for the lake, not the river. Find the depth that matches it and fish there.

The summer decision, step by step

This is for a trout stream from late June through early September, on any day the forecast air high passes 85 °F (29 °C).

1. Check the closures page the night before. A hoot-owl restriction or a full closure makes the decision for you.
2. Read the water in the current where you will fish, and know the afternoon high from yesterday’s 3 p.m. reading.
3. Below 65 °F all day: fish normally. For brook trout, 65 °F is also the day’s ceiling.
4. Afternoon high of 65–68 °F: fish, but shorten everything. Barbless hooks, the fish kept in the water, no photograph in the air. Use a tippet heavy enough to end the fight in a minute: 4X fluorocarbon lands a 16 in (40 cm) trout, on a knot that holds.
5. Afternoon high above 68 °F: fish dawn only. Start in the gray light, keep the thermometer clipped to your vest, and quit the moment the water touches 68 °F.
6. Morning reading already at 70 °F: leave the trout alone. Drive to a tailwater, a spring creek or a lake you can fish deep. Or fish for bass, comfortable at 65–80 °F (18–27 °C), or carp at 70–85 °F (21–29 °C).
7. Write down the reading, the hour and the result. A notebook of afternoon highs tells you when your home water closes next July.

When does the fishing turn back on?

Fall is the trout’s reward for surviving summer. As the water falls back through 65 to 55 °F, browns and rainbows feed in daylight again. Vermont’s fall fishing guide puts the reason plainly: cooling water sets fish feeding heavily to build reserves for winter. The National Park Service puts the brown trout’s optimum at about 50–60 °F (10–16 °C), and a stream dropping into that band in October is at its best of the year.

The relief comes slowly. In Montana the hoot-owl hours come off only when conditions improve, not on the first cool night. On a river without a rule, run the same test backward: the afternoon high has to hold under 68 °F before the trout are yours again, and under 65 °F for brook trout.

The brown trout bite peaks before the spawn, not during it. Virginia’s wildlife department puts the pre-spawn window at late September to mid-November, when male browns turn territorial and chase anything that swims into their water. Its advice is a conehead Woolly Bugger in sizes 2 to 6, dark in stained water and light in clear, worked through the soft water behind boulders, over shelves and along log jams.

The spawn, and the redds

The spawn follows the falling thermometer. Brown trout start as the water drops into 42–48 °F, brook trout at 40–50 °F, and on the Arkansas tailwaters the browns keep at it from late October into the middle of January. Brook trout dig over upwelling groundwater in the headwaters of spring-fed creeks, where at 50 °F the eggs take about 45 days to hatch and in colder water sit in the gravel until January or February.

A redd is a clean oval of lighter gravel, 2–3 ft (0.6–0.9 m) across, in a tailout or at the tail of a riffle, often with a small depression or a mound. Walk around every one, and stay off them after the fish have left: the eggs are still in there. Arkansas Game and Fish warns that pulling a big brown off the redd it guards lets other fish rob the nest, and many trout anglers leave spawning fish alone. On a small wild-trout creek the simplest answer is to fish from the bank until December.

Rainbows follow the spawning browns to eat the eggs that wash out of the redds. That is why an egg pattern drifted well below a redd catches rainbows in November, and why it must never be drifted over one. Lake trout spawn on rocky shoals at 45–55 °F, out in the lake rather than in a stream.

Steelhead run on the same falling thermometer. New York DEC calls them most active at 45–58 °F and says the run slows below 40 °F (4 °C).

Winter is the metabolism rule run backward. Every 18 °F of cooling halves what a trout needs to eat, so a rainbow at 40 °F feeds about half as often as one at 58 °F (14 °C). A South Carolina DNR biologist draws the line at 50 °F: below it the feeding slows noticeably, and his one-word instruction for fly anglers is “dredge”. Oregon’s fish and wildlife department tells winter anglers to sleep in. The best fishing runs from late morning to mid-afternoon, in back eddies, off-channel water and the inside of current seams, with midges of size 16 and smaller on 5X tippet. A trout in 38-degree water will not move far for a fly, so cover each lie before moving on.

Where are stream trout as the water falls?

The same stream from late summer into winter, read from the top down. A reading of 55 °F in October is not a reading of 55 °F in April: the fish are fatter, the browns are territorial, and the gravel is about to hold eggs.

The direction matters as much as the number here too. A stream falling through 50 °F in November is heading for the redds; one climbing through 50 °F in April is heading for the best fishing of the year.

The trout hub tells the five trout apart, and the species pages carry each fish’s biology.

Free PDF · 16 pages

Stop guessing. Know what's biting before your first cast

A whole Saturday on the water with nothing to show for it. One reading tells you who's feeding.

The Water Temperature Fishing Chart. Take one water temperature reading, find it on the chart, and see which of 26 freshwater fish are spawning, feeding hard or slowing down.

• Where bass, crappie, bluegill and walleye sit, and what to throw. Trout: the reading where you stop.
• Why a 3 ft drop beats a cold front, and what to throw each day of the front
• The three thermometer mistakes that make a reading lie

The chart's numbers come from state fish and wildlife agencies and fisheries research: 61 sources, each listed on the site.

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No card, nothing to buy. Confirm with one click and the PDF is on its way, one version for your phone and one to print, yours to keep. Then a few short emails and one a week on what's biting, with an unsubscribe link in every one. Privacy.