The ocean garbage patches are not solid ‘islands’ of trash. Rather, the plastic is dispersed, forming massive ‘debris fields’. But that does not mean these areas aren’t highly polluted and don’t require cleaning up. The average concentration of the Great Pacific Garbage Patch is around 60 kg per square kilometer, and peaks at several hundred kg per square kilometer. For comparison: a few hundred kilometers from the patch you’d struggle to find values of 0.1 kg per square kilometer. A summary of the science of the Great Pacific Garbage Patch can be found here and more details on the trash island misconception here.