This organisation is more specifically focused on river/ocean plastic removal right now. The ocean conservancy is another organisation that, amongst a wide variety of ocean-related efforts, also deals with trying to improve legislation/etc further upstream (pun intended :P).

Both do pretty impressive work! I personally find The Ocean Cleanup's more narrow focus at times useful, since it makes them a bit more defensible. Meanwhile finding exactly what the ocean conservancy is even doing is a little difficult because they touch a ton of ocean related things.