It is certainly true that large amounts of plastic works it way down are rivers and out to sea, and it is important that we remove these pollutants before they reach the sea as soon as possible.
However much of the biggest, and most problematic plastic pollution in the sea comes from discarded fishing gear. Made from artificial materials including a great deal of plastic (so ways to last longer) when discarded they can last for years entangling whales and turtles among other wildlife.
It is estimated that 640,000 tons of of this gear is dumped at sea each year, and while it’s only accounts for around 10% of the volume of plastic that makes its way into the sea, it is the vast majority of large plastic which can cause entanglement problems to marine mammals (due to its size and the fact that it was made for catching fish originally).
The great Pacific garbage patch contains around 42,000 tons of plastic around 86% of which is abandoned fishing gear. While we have the exciting prospect of Boyan slats ocean cleanup, it needs to become uneconomical for fishing gear to be discarded at sea. Worldwide we may find that the only way to stop this this is too fine fishermen for their lost equipment- while this would be difficult to implement it may be the only way to make it financially unacceptable to abandon equipment at sea.