It depends very much in which region you are investigating. In regions with lakes of icing certainly the water temperature is not going lower than 0 (when lake is salty can be also cooler, but not much). Thus, anyhow your air temperature can be -10 C, the water temperature will not go down, but  if lake is too shallow it starts freezing and then relation disappears at all.

Thus, climatic region is very important.

Second, the depth of lake. In both hot and cold regions, the amount of heat  to absorbable in water depends very much on depth of water body.

Thus, these points mentioned does not allow to have relation between air and water temperature suitable for all lakes in all climate regions and independently from the depth of lake.

Thus, can you ask more precisely? Which lakes and where you are investigating?

Dear Veljo,

Thanks for your contribution, my case is in Iran and its name is Urmia Lake. It's about superficial one of approximately 11 m depth and is world third saline lake. The climatic meteorology of the region is of cold-arid mountainous division.

Regards.

Hello,

Beside modeling of the energy budget of the interface water-atmosphere for which you will also need meteorological data the simple empirical way is to conduct measurements of both water and air temperatures for enough long period in order to include extremes. Then you may use any statistical software to fit an equation. The third way is by using the analogy with an already studied case having similar climatology. 

Hello,

Of course, for the time being i have just climatic data of the region and need for those data for that region water temperature. I require the obtained relation having the same meteorological situation.

a paper Estimating Stream Temperature from Air Temperature:

Implications for Future Water Quality for relationshep between stream and air tempretuare

Respected Ms. Maryam Hafezparast

Thanks a lot for the clues and suggesting the related paper. 

Regards.

You can read the following paper:

Water temperature prediction in a subtropical subalpine lake using soft computing techniques

https://www.researchgate.net/publication/307862369_Water_temperature_prediction_in_a_subtropical_subalpine_lake_using_soft_computing_techniques

Article Water temperature prediction in a subtropical subalpine lake...