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Heat Wave!

Judy Van Put
Posted 7/6/21

The end of June brought a record-breaking heat wave all across the country, and the month ended with area rivers and streams at below average flows and high temperatures.

The Beaverkill at Cooks …

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Heat Wave!


The end of June brought a record-breaking heat wave all across the country, and the month ended with area rivers and streams at below average flows and high temperatures.

The Beaverkill at Cooks Falls had consistently registered below the 106-year average flow all week; on June 30 the flow was measured at just 122 cfs, which was below the (mean) average on this date of 436 cubic feet per second.

Water temperatures at the beginning of the week began with a low of 60 degrees but had steadily risen each day until the afternoon of June 30, when the Beaverkill was recorded at 83 degrees Fahrenheit! Needless to say, anglers were not seen on the Willowemoc and Beaverkill during the last days of the month; hopefully the beginning of July rains will provide respite for our waters and the trout.

Some may wonder why there is concern about warm temperatures and trout.

All fish species have preferred water temperatures: with largemouth bass, for example, preferred temperatures are from about 65 to 75 degrees Fahrenheit. For trout, the preferred temperatures (and maximum growth) are generally concluded to be best between 45 and 66 degrees F. However, trout do feed both above and below these temperatures.

Trout are cold-blooded animals; their body temperatures change to the temperature of the water they are living in. Water temperatures directly affect their growth, reproduction and survival.

Fortunately, temperature changes on most of our streams and rivers do not occur rapidly. Trout survival often depends on the rate of temperature change and how well the trout are acclimatized, as well as the genetic strain and size of the fish. Some trout can survive temperatures in the mid-80’s but they cannot survive them for long.

Trout can live at temperatures above 68 degrees Fahrenheit only if the water is well saturated with oxygen. Temperature tolerance decreases as the amount of oxygen in the water decreases - colder water is more highly saturated with oxygen than warmer water.

Brook trout are less tolerant of high water temperatures than are browns or rainbows. This is one of the reasons brook trout do not reside in the lower reaches of our rivers, which tend to be warmer than the headwaters.

Lethal limits for brook trout are generally accepted to be 77 degrees Fahrenheit, while the lethal limit for browns is usually placed in the mid-80s; for rainbow trout it is slightly higher. Remember that these are lethal limits for trout that are simply residing or resting in the stream.

When water temperatures rise above 75 degrees F., trout will seek out and sometimes concentrate in spring holes in the stream and off tributary mouths. They do so because they are in distress, either from insufficient oxygen or high water temperatures. Trout are very vulnerable at these times, and serious exertion under such conditions may be fatal.

The trout population of a stream or river can be seriously impacted by fishing for them under these conditions; it offers no real sport, rather it is taking advantage of their discomfort. Most of these highly vulnerable, concentrated trout that are exploited in this manner will die, even if they are released.

When temperatures are high and stream flows are low, such as we experienced last week, it’s a good idea to carry a thermometer in your fishing vest to monitor water temperatures.

If temperatures are too warm, the first and most obvious thing to do is to travel upstream, where the water may be more shaded and be better influenced by cold springs and cooler tributaries. Another tactic would be to fish a smaller, cooler tributary, as many offer good fishing, especially for wild trout.

When water temperatures rise on the Beaverkill and Willowemoc and trout fishing is not an option, check out the “tailwater”streams that receive cold water releases, as these streams can offer a “second season” during the summer months, providing excellent trout fishing when natural flowing streams and rivers get too warm.

Tailwaters occur on many rivers which have been impounded for hydroelectric power or water supply, such as the NYC Catskill Reservoirs, where during the hot summer months water is released from the bottom of the reservoirs and is generally colder than the water entering the reservoir.

Taking water temperatures on tailwater streams is also important, as many of these waters do not receive steady releases. Flows can fluctuate dramatically causing significant changes in water temperatures; and if a reservoir is spilling, for example, the surface water entering the stream below will not be cool.

To take a water temperature, wade into the stream at a reasonable distance from the stream bank; it is not necessary to wade to the middle. Hold the thermometer completely under water by a few inches, making sure you are in flowing water, and shield it from direct sunlight by shading it with your body.

Leave it in the water long enough to “steady” on a reading – this will take about a minute for a mercury thermometer, longer for an alcohol (red liquid) thermometer – checking the temperature while the thermometer is still under water, as on a hot day it will rise quickly once it reaches the air.

Understanding water temperatures and their effect on trout is essential, and is important to know when fishing for trout. This can determine not only whether you should fish, but also whether or not you can expect to catch trout.


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