Meet the Moss Animal, one of only a few one-celled animals that live in freshwater rivers and ponds. This jelly blob mass looks like something out of a swamp monster movie, but its very nature is innocent. It acts like a water purifier and helps keep fresh water filtered.
With a feather-like retractable arm extending from the body, the bryozoan will filter like you see similar feather-like coral filters in the ocean. Bryozoans mostly eat algae, bacteria and other small one-celled animals.
They have existed for millions of years and many species are found as fossils, especially the seawater species that make a calcified enclosure that fossilizes very well. It is believed that the freshwater species are more recent additions to the family. On a particular river, I tend to find this in the backwater areas or the lungs of the river where filtration and digestion of detritus usually happens.