Surface Temperatures. —During the winter, from the latter part of December to the breaking up of the ice in the spring, the temperature of the water under the ice is 32 F. The water then warms at a uniform rate to 72 F.
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In winter, the exact opposite happens since the lakes are covered with ice. Most of the water under the ice is 39 Fahrenheit; however, there is a thin layer of water under the ice that is colder than 39 and therefore less dense.
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.
Do not attempt to cross this ice. Watch for rivulets flowing on the ice or streams flowing under it. Even when the surface looks solid, a current under the ice causes erosion from below.
Three distinct layers develop: The top layer stays warm at around 65–75 degrees F (18.8–24.5 degrees C). The middle layer drops dramatically, usually to 45–65 degrees F (7.4–18.8 degrees C). The bottom layer is the coldest, staying at around 39–45 degrees F (4.0–7.4 degrees C).
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.
When is it safe to walk on a frozen lake? As a general rule of thumb, ice is safe to walk on when there is 4 inches or more of clear ice. It is important to understand that different types of ice varying in their strength. Clear blue or black ice is the strongest.
Only the top layer of the lake or river freezes. Underneath the frozen upper layer, the water remains in its liquid form and does not freeze. Also, oxygen is trapped beneath the layer of ice. As a result, fish and other aquatic animals find it possible to live comfortably in the frozen lakes and ponds.
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.
Thus, the ice layer at lower temperature floats over the water below it. Due to this, the freezing of water into ice occurs continuously from the top towards the bottom.
Water is a great insulator and good at holding heat, which is why the lake temperature doesn't fluctuate much day to day like the air does. Therefore, below freezing temperatures are needed for a week or more to form ice on a large lake.
Your lake or pond won't fully freeze when the water temperature drops below 32 degrees. You should also consider what outside factors may be affecting your body of water. How much sunshine does the area get?
If you can see the ground through the ice, then there's going to be warmer water under it. Out in the middle, the ice grows thicker over the cold dark depths. Also, ice always melts away from the shore first.