Understanding Stillwater Trout – Part 4: Seasonal Changes

In the previous article we covered the in which trout live.  However a lake is not static, and changes with the seasons.  If we don’t understand those changes, and how they impact the trout’s behavior, then we will not know the right location to fish for them.

Some things, like shoreline or structure tend not to change with the seasons – that is unless the water level significantly changes.  But temperature and oxygen content – both very important to trout – are greatly impacted by seasonal changes.

Below I’m going to describe a lake that is fully impacted by the seasons.  However lakes are all different.  Where a lake is will control how if it experiences the full cycle.

For example a high mountain lake may have a more minimal summer impact, and therefore not have a thermocline develop.   Conversely a lake located in the middle of Texas will not get cold enough to develop ice.

So you may need to adapt this pattern to fit what you observe at your favorite trout lakes.

The seasons form a cycle, each having its primary characteristics which define how it impacts the trout.

Stillwater Lake Cycle


This is the coldest time of year, and the water is also cold.  The lake is covered by a sheet of ice.  The ice limits the amount of surface interaction and light the water below receives, because of this the oxygen is limited.

The trout will be sluggish, as their metabolism is slowed by the cold temperature.

The lake may experience what is called a “winter kill” where many fish die off, due to a lack of oxygen in the water.


As winter gives way to spring the lake starts to warm, starting with the top of the water column.  This will eventually cause “ice out” to happen, where the ice starts breaking up.

The trout start to become more active as the temperature and oxygen levels come back up.  On especially warm days the fish may have a feeding frenzy as they attempt to recover from winter.

Eventually the water will continue to warm and the upper layers will achieve that mid 50s temperature that trout love.

When the happens be prepared to see a lot of surface activity as the trout enjoy that warmer water near the surface, and actively feed a lot.


Spring turns to summer and the heating continues.  Soon the water at the surface becomes too hot for trout.

A thermocline begins to form, separating the hot water above from the cold water below.  As the water above continues to heat up, the thermocline will move deeper and deeper.

The water above the thermocline is too hot for the fish, but the water below has low oxygen due to the barrier of the thermocline.  Understanding the thermocline is very important to understand as it greatly impacts the fish’s location.  You can read more about it here.

The trout will follow the thermocline down and spend much of their time around it.  They will leave the thermocline occasionally to actively feed elsewhere.

If the lake gets too hot and there isn’t a deep section for trout to retreat to, then it may experience “summer kill.”


Fall brings with it colder temperatures.   The water starts to cool.

If this cooling is gradual enough then the thermocline will slowly disappear.

If it happens faster then the lake will “turn over” where the now colder and denser water above trades places with the colder water at the bottom.  When this happens the trout will stop feeding for several days until they adjust to the new conditions.

Regardless if it is gradual or sudden, the lake will reach a point where it is all the same temperature.  This means the trout will no longer have a preferred depth based on temperature.  They will focus on areas where food are, as they prepare their bodies for winter.

Back To Winter

Winter now arrives again.  The water will continue to cool, and eventually start to form ice at the surface.  The cycle is now ready to begin again.

Winter Cutthroat from Lake Sammamish
Winter Cutthroat from Lake Sammamish


We’ve covered how the changing seasons impact the temperature of the water, and it’s impact on the trout.  Sluggish in the winter, active near the surface in spring, hanging out in the depths during summer, and then following the food in fall.

Next up in the series we will consider a typical western Washington lake and detail .

For more information about fishing for trout, please check out the trout page.

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