The white and black plummage of loons is their breeding plummage. In winter loons molt to a dull grey and white plummage which does not have the elaborate patterns of summer. Immature loons are also this dull grey and white color. Loons are visual feeders which means that they need to see their underwater prey to be able to capture it. For this reason they need fairly good vision and clear water.
Loons have difficulty capturing prey on lakes with heavy algae blooms or very dark staining.