Turns out most of it is bigger, but still not easily visible (I was definitely one of the people that thought it was giant heaps).

the patch is a widely dispersed area consisting primarily of suspended “fingernail-sized or smaller”—often microscopic—particles in the upper water column known as microplastics.[4]

While microplastics dominate the area by count, 92% of the mass of the patch consists of larger objects. Some of the plastic is over 50 years old, and includes items (and fragments of items) such as “plastic lighters, toothbrushes, water bottles, pens, baby bottles, cell phones, plastic bags, and nurdles”.

Wikipedia