How to check water temperature
Take a reading at the depth you're actually fishing, and use the trend through the day to decide how to present.
Last reviewed 26 September 2026 · Editorial policy
What this skill is for
Fish are cold-blooded: water temperature sets how fast they digest, how far they'll move and how aggressively they feed. The same lake holds several different temperatures in the same afternoon, so a single surface reading can be misleading.
What you need
- A fishing thermometer (a floating type is fine)
- A lanyard or a clip
- Somewhere to note the readings
Step by step
- 01
Clip it on and cast it out
Attach the thermometer to a lanyard under the float or on a lead, cast to your swim, and leave it for a minute so the reading settles.
- 02
Read it at the depth you're fishing
Surface water and bottom water can differ by several degrees, especially in summer and on windy days. Take a surface reading and a bottom reading and compare them — the difference often tells you which layer to fish.
- 03
Note the trend, not the number
A slowly rising temperature usually wakes fish up, particularly in spring and late autumn. A sudden drop — cold front, overnight flip, heavy rain — usually shuts feeding off for a while.
- 04
Compare with the species
Each species page here lists the conditions that suit it. If your reading puts the water near the cold end of that range, expect a slower presentation; nearer the warm end, expect fish to move and take a moving bait.
- 05
Adjust depth and speed to match
Cold water: fish the deepest, most stable layer, slowly. Warm water: fish early and late, shallower, faster, and follow the shade and the oxygen.
Where it goes wrong
- Taking only a surface reading and assuming it represents the swim.
- Checking once at the start of the session and never again.
- Chasing a number instead of watching what the fish are doing.
- Assuming a shallow bay and the middle of the lake are the same temperature.
Related guides
Common questions
What do I need for check water temperature?
A fishing thermometer (a floating type is fine), A lanyard or a clip, Somewhere to note the readings. Nothing specialist beyond that — if a step needs something extra it is listed in the guide itself.
What is the most common mistake with check water temperature?
Taking only a surface reading and assuming it represents the swim.
How do I know check water temperature is done correctly?
You know whether the water is warming or cooling, and you've fished at least two depths to see which one the fish prefer.