Based on the second link you gave, I would say it looks most like Baby Pondweed (Potamogeton pusillus). Although a close second would be Bushy Pondweed (Southern Naiad). I don't think it's Sago. I took some images I took last summer which you can see in this post: https://forums.pondboss.com/ubbthreads.php?ubb=showflat&Main=42894&Number=559830#Post559830.