Inventor and entrepreneur Boyan Slat made waves some years ago by introducing a device that could potentially remove floating trash in the ocean. The device acts as an artificial coastline that floats in the middle of the ocean. The device passively collects trash (e.g., plastics) that float at or near the surface of the ocean.
Netherlands has granted the inventor a patent for a "floating barrier adapted to move freely along the surface of the water... a submerged part connected to the floating barrier adapted to providing a difference between the speed of the floating barrier along the surface of the water and a speed of the objects floating on".
According to the patent specification and the figure above, the "submerged part"  of the device slows the floating barrier  so that the floating barrier moves slower than the junk  that it collects. This helps junk swim into the barrier and stay within it. Drifting anchors can be integrated into the submerged part to help drag the floating barrier (slowing it down further).
This patent appears to relate to an improvement in the cleanup device that is touted in a recent press release on The Ocean Cleanup's website: https://theoceancleanup.com/press/press-releases/the-ocean-cleanup-successfully-catches-plastic-in-great-pacific-garbage-patch/ which describes how slowing the barrier down has helped make it more effective.
The press release states that "The aim of System 001/B was to trial modifications, which addressed known complications, primarily aimed at correcting the inconsistent speed difference between the system and the plastic. Consistency was achieved by slowing down the system with a parachute sea anchor, allowing for faster-moving plastic debris to float into the system. Once this main challenge was resolved, prominent plastic overtopping was observed – becoming the next technical challenge to solve. Due to the modularity of System 001/B, a modification to increase the size of the cork line was designed and implemented while the system was offshore. With the new cork line, minimal overtopping is now being observed, thus allowing the system to capture and concentrate plastic."
Great to see such thoughtfulness go into helping clean up the ocean.