(AP) -- Scientists say more than 150 invasive species have been found in the Great Lakes, the largest surface freshwater system in the world, and more are threatening it. Here's a look at some of those species:
-Zebra mussel, a mollusk first brought to the Great Lakes by oceangoing ships and spread by recreational boaters. The mussels filter vast amounts of water, removing nutrients needed by native organisms that fish feed on.
-Round goby, a bottom-dwelling fish native to Eurasia. It was found in 1990 in the St. Clair River, which connects Lake Huron to Lake St. Clair. The voracious eaters have spread to lakes Erie, Huron, Michigan and Superior.
-Eurasian ruffe, a spiny fish that grows and reproduces rapidly, was found in Duluth Harbor on Lake Superior more than 20 years ago. The fish have also been found in Lake Huron. Experts say they were likely transported in the ballast water of freighters on the Great Lakes.
-Asian carp, which can grow to 4 feet long and 100 pounds, were released into the Mississippi River basin in the early 1990s. They're now in the Illinois River within 50 miles of Lake Michigan. Researchers fear they would displace native fish, disrupting the lakes' ecology and severely hurting the commercial- and sport-fishing industries.
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