Pollution due to coal burning most frequently tends to affect lakes by  -

Pollution caused due to the burning of coal most frequently tends to affect lakes by increasing the acidity of the lakes.

Explanation:

Burning of fossil fuels like coal releases sulfurous gases into the atmosphere. These gases get mixed up with the water vapors to form acidic clouds. Later when precipitation occurs, the water that pours down from such clouds contains acidic properties. This water mixes with the water in the lakes through direct precipitation over the lakes or through the runoff water that eventually mixes with the lakes and rivers.