Freshwater Jellyfish? Are they Real? Native or Invasive?

Craspedacusta sowerbyi, or peach blossom fish or simply freshwater jellyfish, are indigenous to the Yangtze River in China and were first observed in Vermont in 1999. Since 1999, freshwater jellyfish have been spotted in several Vermont lakes, ponds, and river across the state, so how were they introduced and are they a threat?