Final answer:
Glacial lakes are most commonly found in mountainous regions due to the retreat of glaciers that once moved through these areas.
Step-by-step explanation:
Glacial lakes are a common feature in mountainous regions where glaciers have previously advanced and retreated, leaving behind depressions that fill with water. These lakes are not typically found in desert regions, coastal areas, or tropical rainforests, where conditions for glacier formation and movement are not present. Notably, glacial valleys or troughs along coasts can fill with a mix of seawater and freshwater, but these are more specific scenarios related to past glacial activity.