Found this in a small river in Gdańsk, Poland - any clues?

Is this eggs of some kind? Is it alive?

I was playing disc golf and my disc was lost in water in a river for a few days. Someone returned it to me and this... thing... was on it - I wonder if it's just some leftovers or actually an organism?

It seems to have some circles and an orange dot in each circle, while it's mostly transparent... so interesting