A band on the graph is an observation to investigate. Record what the display showed, the settings, the depth and the time. Use separate measurements to answer a separate question: how does water temperature change with depth?
Follow the values down
USGS explains how lake temperature can vary with depth and how seasonal warming and cooling affect mixing. The exercise here compares entered temperatures. It does not infer dissolved oxygen, label a layer habitable, or locate fish.
In the fictional practice profile, temperature falls from 84°F at eight feet to 75°F at twelve feet. That is nine degrees over four feet, or 2.25°F per foot. The orange band marks that sampled interval. It is not a claim that the entire lake has that boundary.
Open the temperature explorer →Take the uncertainty with you
Two widely spaced readings can miss what happens between them. Take additional measurements around a change, keep instrument limitations in mind, and retain the original values. A flatter profile can be informative too; the exercise does not force a thermocline result.
Check your understanding
What does the highlighted interval establish?
Source: USGS Temperature and Water · Checked September 6, 2026.