Hi Lea, welcome to the group! The reason bodies of water and their nearby surroundings do not change temperature very rapidly is due to the high specific heat of water, 4.184 J/goC (1.00 cal/goC). This means that it takes 4.184 joules of heat energy to raise the temperature of one gram of water by one degree Celsius (or Kelvin). This is a much larger specific heat compared to most other substances. For instance, iron metal has a specific heat of only 0.45 J/goC, so less than half a joule of heat energy will raise the temperature of one gram of iron by one degree Celsius. Thus, when iron and water lose the same amount of heat, the temperature of the iron decreases by a much greater amount than the water does.
Lakes, soil, and water absorb heat energy from the effect of sunlight during the day, and cool down at night, but the temperature of the lake will change much less. The surrounding area on the shores of the lake, being in close proximity to the lake, are more affected by its temperature, but the farther away you are from the lake, the less its stabilizing temperature effect will be felt.
Rock warms up quicker than water because the specific heat of rock is relatively low compared to water. This means that it takes more heat to raise the temperature of water by 1 degree centigrade (C) than rock. In fact five times more heat is required to heat up water when compared with rock. The specific heat of water is 1.00 which is much higher than rock which has a specific heat of is 0.2. Water requires a lot of heat to warm up and must lose a lot of heat to cool down. A great of heat is required to increase the temperature of water so in early summer in temperate regions lakes tend to be cooler than the land. Large lakes and the sea are slow to warm up even in the summer due to the vast amount of heat energy they require to warm just a few degrees.
SPECIFIC HEAT is defined and measured by the number of calories required to raise 1 gm of material by one degree centigrade. One calorie will heat 1 gm of water 1°C, but would heat 1gm of rock 5°C, or 5 gm rock 1°C.
Hope this helps!
Steve
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