The Great Pacific Garbage Patch. 

The main problem in the eastern pacific ocean is The Great Pacific Garbage Patch (GPGP). This garbage patch that resides in the pacific ocean is made up of various different plastics ranging from 50cm to just a few mm in size and today in total the estimated weight of it is 80,000 tonnes, which's the equivalent of 500 jumbo jets and its estimated that there are 1.8 trillion pieces of plastic in the patch and due to its size, The GPGP has many causes and effects. 

When we first discovered the GPGP we didn't know what caused it but today we know one of the many different causes is of the GPGP are gyres, Which circulate ocean water driving ocean currents and moving things around like many plastics that float on the surface of the water. And in certain places, these gyres converge and eventually created the plastic soup that we now call the Great Pacific Garbage Patch.  Another one is rivers, specifically 10 of the worlds major rivers are estimated to supply about 90% of the plastic that reaches the ocean. 

Sadly one effect of the many that the GPGP poses is the threat they pose to sea life; for instance, sea birds like seagulls eat the plastic and inside their stomach, it doesn't break down and it eventually fills their stomachs and that causes them to not get the nutrients that they need to survive. Another one is that these plastic are relatively new and we don't really know definitively how long it will take for this plastic to break down but even if they do break down they'll turn into miro plastics and miro plastic have been found in the stomachs of many fish that humans consume and there are fears that this plastic will break down, even more, creating nano-plastics that can get into the muscle tissue of the fish that we eat, today we don't fully understand the health implications this will have on marine life and humans.