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Water temperature is an important factor to take into account when searching for fish. At times, it can help you narrow your search for specific species.  Fish are cold blooded which means they cannot internally increase their own body temperature but they can and will move to seek a temperature that is not only more comfortable but more stable.  Think about being in a room and someone constantly turns the heat up and then cools it down with AC.  You would not be very comfortable and neither does the fish ,so they will sometimes sacrifice a warm temperatures for a more stable one.  Not all fish prefer the same temperature.  I’m not sure how scientists figured it out but maybe fish answered an online survey.  Here is a chart of preferred temperatures by fish species.

https://fishhawkelectronics.com/blog/water-temp/

Temperatures shown in degrees Fahrenheit

To  find the ideal temperature , I use my fish locator to 

To find the water temperature, I use my fish locator which has a temperature sensor in the transducer.  This will only give you surface temperature.  Before making a determination of water temperature , allow your transducer to acclimate to the new temperature of the water.  Many people will look at the water temperature right when they get in the boat but it takes several minutes for the transducer sensor to give an accurate reading.  I also use the Fish Hawk depth probe to find the temperature of the water at depth and form a temperature profile.

To understand the dynamics of water temperature there are a few principles you need to understand.  First is that cooler water is denser than warmer water.  Secondly, energy always moves from higher temperature to lower temperature.  If you see lakes “steaming” in the morning after a cool night it is because the water is losing energy to the ait which causes water vapor over the water. Water temperature also affects the dissolved oxygen in the water that aquatic animals need to breathe.

 

Immediately following ice out the entire water column is close to freezing or about 33-34 degrees.  As the upper layer warms to 39 degrees (the densest water ever is) this layer will sink and cause what is called spring turnover.  It is rapid and will cause the water to be dirty.  When turnover is complete the sediment that was mixed into the upper layers will settle and the lake will clear.  Most people never see this ph

The next phase is the most misunderstood.  If water were allowed to warm with sunny days with the same light intensity there would develop a warm layer over a cold layer.  In the separation between these two layers, the temperature drops rapidly because sunlight doesn’t penetrate much deeper. The layer above is less dense than the layer above the thermocline and these layers usually don't mix.  In most lakes fish can’t live below this line as there are no plants or algae living and producing oxygen.  Beneath the thermocline, dead plants and animals fall to the bottom and decompose, using what little oxygen is available.  If you determine the thermocline you should fish above that depth as fish can’t survive without adequate oxygen.

 

But nature is seldom a static force and turbidity, winds and cold nights play havoc on this tidy scenario.  Water with a dark stain from tannic acid leeched from needles and leaves or suspended sediments will absorb the sun’s energy more than pure clear water.  These lakes will warm quicker in the spring and should be your choice during opening day during a late spring. 

 

Wind also pushes the warmer  less dense water to the windward side of the lake. In the spring,when water is first warming, only the top foot or so of the water column warms.  Steady winds will push the less dense warmer water to the opposite side where the wind is coming from(leeward side). This will cause the deeper cooler water to move to the surface of the windward side of the lake. (The side where the wind direction is coming from.).  In the spring when water is still cold, always fish the side of the lake where the wind is blowing into.  The water temperature will be several degrees warmer here and fish will gravitate toward this warmer water.  One early spring day we were fishing a lake where the launch was on the north side of the lake.  Wind had been blowing into the shoreline for several hours from the south.  The water temperature was s1x degrees warmer on the north vs the south side of the lake.  My son caught his limit of walleyes and a muskie before I even started the motor.  Many fishermen launched a flew past us to the otherside of the lake as we pulled fish out of the net.

 

Wind is also a factor in long windswept sections of the lake.  When wind blows the length of a lake for an extended period of time the warm water is pushed to the lee side of the lake and cooler water from below upwells on the windward side.  Lake Michigan shore fishermen understand this phenomenon well as it brings cooler water closer to shore and the alewives follow the cooler water and the salmon are not far behind. This mixing of all layers of the water column results in a consistent temperature as evidenced by a recent temperature profile from Big Saint Germain lake where the water temperature was within one degree from top to 25 feet. This allows fish to move deeper if food is available. Perch will move to the mud basin of the lake and predator fish follow.  Find a way to get to these fish as they are willing biters.  They are there for one reason, to eat.

 

Lastly , inconsistent temperatures will cause mixing of the water column.  Many people think the only time water mixes is during turnover.  I explained one way it can mix with wind but another method is when temperatures drop overnight or over a period of days.  In both cases, water loses energy to the air. (When you see lakes “steaming” in the early morning, you are seeing the lake lose energy and drop in temperature.  Cold water is denser and it will sink.  The lower water column will rise to replace that void.  Shallow water changes temperature quicker than deep water just due to the volume of water.  On cold spring days or when the overnight temps are cold, avoid fishing the shallows until mid day when the sun has a chance to warm. Fish will either bury themselves in the weeds or suspend in deep water when this happens.  Conversely, I have seen walleyes in two feet of water in the morning under trees.  They are seeking a cool respite from the hot water of summer.  In the fall daily temperatures can fluctuate 40 degrees sometimes.  Water doesn't change temperature as easily as air.  Air changes temperature more than four times faster  than water.  With that said,  a ten degree swing in water temperature is uncomfortable to fish.  They will seek the comfort of deep water for stability which is why during  late fall fish will move deeper.

 

Using this knowledge of water temperature will allow you to predict where fish are in a system.  It is then up to you to present your bait to the fish in a manner where they will bite.

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