Does lake water get warmer the deeper you go?

In summer, the top of the lake becomes warmer than the lower layers. You've probably noticed this when swimming in a lake in summer - your shoulders feel like they're in a warm bath while your feet are chilled. Since warm water is less dense that colder water, it stays on top of the lake surface.



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In summer, the top of the lake becomes warmer than the lower layers. You've probably noticed this when swimming in a lake in summer - your shoulders feel like they're in a warm bath while your feet are chilled. Since warm water is less dense that colder water, it stays on top of the lake surface.

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Lakes have layers Water temperatures also play a role in water density. Warm water is less dense meaning it is lighter and stays toward the top of the lake. The colder, heavier water is found at the bottom.

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When water cools down to 0 degrees Celsius (0°C), ice begins to form and floats on top of warmer water; water at the bottom of a lake or river is typically 4°C (if it is not frozen). During the summer, the opposite occurs as warmer water floats on top of colder water. Many factors can affect water temperature.

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Because water warmer than 40oF is more buoyant than cooler water, spring warming creates a shallow, warmer layer of water late in the day on the downwind side of a lake. Other factors being the same, the north side will warm more quickly than the south side of the lake.

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But, in winter some lake surfaces can get very cold. When this happens, the surface water becomes more dense than the deeper water with a more constant year-round temperature (which is now warmer than the surface), and the lake turns, when the colder surface water sinks to the lake bottom.

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If you are getting 50-55 degrees Fahrenheit, turnover may be nearing or just starting. By 45-50 degrees Fahrenheit the lake is making the change rapidly, and fall turnover is complete at around 40.

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Most lakes and ponds don't completely freeze because the ice (and eventually snow) on the surface acts to insulate the water below. Our winters aren't long or cold enough to completely freeze most local water bodies. This process of lakes turning over is crtically important to the life in the lake.

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Since water is good at holding heat, the more water there is, the more heat it will hold. This is why large deep lakes take longer freeze and melt than small shallow lakes.

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Deep lakes only mix in spring and fall, and the bottom of deep lakes stays cold and dark because light cannot reach the bottom. Shallow lakes, in contrast, mix all summer because light reaches the bottom of the lake and warms the whole water column.

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