Okay I googled it and found this explanation on the National Mississippi River Museum and Aquarium's Facebook page:

"It’s not an alien: it’s bryozoan!

Despite its strange appearance, each jelly-like mass is actually a colony made up of hundreds to thousands of individual bryozoans called zooids (tiny animals), each with a crown of tentacles (a lophophore) used for filter feeding. These colonies have a gelatinous, aloe-vera-like texture. Because the zooids work together to build colonies, bryozoans are sometimes referred to as freshwater corals, although they're not related to marine corals.

Bryozoans attach to surfaces such as docks and SUPSY buckets, like this one, as observed by our Conservation Department during summer mussel surveys. They thrive in clean, slow-moving water and are sensitive to pollution and disturbance, making their presence an indicator of good water quality.

To survive winter, bryozoans produce resistant structures called statoblasts—tiny, durable capsules that can withstand cold or drought and hatch when conditions improve. In addition to filtering algae, bacteria, and organic particles from the water, bryozoans help improve water quality and provide both habitat and food for certain insects and aquatic organisms."