What causes that “root beer” color in some lakes?
Sometimes described as root beer, coffee, tea, or bog stain, such coloring is natural for many waters in northern Wisconsin. The coloration is not harmful and results from incompletely dissolved organic materials, sometimes referred to as tannins, which come from the decomposition of wetland plants in the watershed of the lake. Often, the greater the amount of wetlands in the watersheds, the darker the color of the water. Since the predominant land type in the watersheds of northern Wisconsin lakes is often a mixture of forests and wetlands, this can result in many lakes having this dark coloration.
