|Tom Pelletier's article from 2001.
||Gen-yu Sasaki's great page with pictures and explanations.
||Here's a nearby page on "Things that don't belong where they are."
||Dr. Terry Peard at Indiana University (of Pennsylvania!) collects information and has a very good web page about these.
||A Boise, Idaho Girl Scout troup found some jellyfish.
||Encyclopedia Brittanica article.
||The US Geological Survey page, which explains where these jellyfish came from, and has a map of where they're found now.
||A Google Search for "Freshwater Jellyfish".
||Getting off topic a little, in 2017 there's a similar saltwater phenomenon happening in strange numbers. "Pyrosomes", which are colonies of zooidsa>.