The great pacific garbage patch will be difficult to physically clean up because

The Great Pacific Garbage Patch is an environmental problem of the Pacific ocean water. It is accumulated with a trash of 10 meters deep non-degradable plastics. These plastic wastes can trap marine animals and contaminate the quality of water.

The Great Pacific Garbage Patch will be difficult to physical clean up because it actually lies in the international water, and no single nation is responsible for it's creation, also the filtering out of the plastic will effect the marine animals and diversity of marine phtoplanktons and zooplanktons.

explanation:

for  example, forests have higher evapotranspiration than other ecosystems,  such  as grasslands, because of their deeper roots and greater leaf area. thus forests have a net moistening effect on the atmosphere and become a moisture source for downwind ecosystems.