Where to Find Ocean Plastic
Clouds not Islands
Despite the common public perception of the patch existing as giant islands of floating garbage, its low density (4 particles per cubic meter) prevents detection by satellite imagery, or even by casual boaters or divers in the area. This is because the patch is a widely dispersed area consisting primarily of suspended "fingernail-sized or smaller bits of plastic", often microscopic, particles in the upper water column known as microplastics.
The reason the patch exists is two fold:
Humans do not look after their waste properly!
The ocean currents concentrate floating / suspended debris over time in particular areas.
There are numerous other ocean gyres around the world which are doing similar things, so although the Pacific Garbage "Patch" gets the most press, there are likely dozens of smaller patches around the worlds oceans.
Nooks and Crannies
Closer to shore, where potential beach plastic float, there are other currents which control the direction of travel. These currents can create a depositional and erosion environment depending on the type of coastline.
To look for areas of coastal deposition the following features are required:
waves enter an area of shallow water;
waves enter a sheltered area, e.g. a cove or bay;
there is little wind;
there is a good supply of material.
We would suggest that wind will play a role in guiding floating debris (plastic bottles) whilst the waves will dictate travel direction of suspended items (plastic crates).
The above observations would explain why areas of the UK coastline such as the Western Isles and The Isle of Skye, have such large amount of plastic washed up on beaches.
As well as being the cause of the plastic problem, people are also the solution. Many good people will take part in voluntary beach cleaning (whether alone or in groups), and in populated & accessible areas this will reduce the amount of beach plastics. One such Person (with Help from Family) is Jules O'Shea, who probably picks up 100 or more pieces of beach plastic every week. To see other examples search using the hashtag: #2MinuteBeachClean.
The result of this good work is that you will find less ocean plastic washed up on beaches where people can easily access that beach. Rocky coves only accessible by several hours hiking, or accessible by boat only, will have a lot more plastic accumulated upon them.