Researchers have made a startling discovery in Lake Erie -- two species of exotic zooplankton that originally hail from the southern hemisphere.
The U.S. Environmental Protection Agency says this is the farthest north either species has been tracked in the Western Hemisphere.
One of the species (Diaphanosoma fluviatile) is from Central and South America and the Caribbean, whereas the other (Mesocyclops pehpeiensis) is native to tropical and temperate areas of Asia.
Scientists don't know how the zooplankton entered the lake, nor do they know what risks the tiny creatures may pose.
The EPA says zooplankton are highly sensitive to changes in aquatic ecosystems. The kinds of zooplankton found in the water, and the abundance of certain species relative to one another, serves as a measure of biological condition.
"Zooplankton are good indicators of change in nutrient pollution over time because they respond quickly to changes in nutrient input to the waterbody," it says.