Since their arrival in cargo ships that sucked up fresh water in Europe and the Far East and dumped it in the Great Lakes, spiny fleas have reduced the biomass of Daphina so much that algae growth has spiked, and Lake Mendota's visibility has clouded, further impairing a resource on which humans and animals rely. Once people could see their toes in water that was chest high as opposed to about thigh high, said the author of a new study that shows how invasive species like the spiny water flea does a lot more damage than people know.