What is considered the greatest threat to the Great Lakes? 

A)  the spread of alien species 
B)  the increase in commercial fishing 
C)  the dumping of raw human sewage 
D)  the increase in thermal pollution from electric power plants

Alien Species

Alien species, also known as invasive species, are organisms that are introduced to a new habitat where they are not native, often causing harm to the environment, economy, or human health.

Great Lakes

A group of five large, interconnected freshwater lakes located on the border between the United States and Canada, significant for their water resources, biodiversity, and transportation routes.

Thermal Pollution

The degradation of water quality by any process that changes ambient water temperature, typically due to industrial activities like power plants.