Indus --- China, India [2], Pakistan [3]

Yellow --- China

Hai He --- China

Ganges --- India, Bangladesh [4]

Pearl --- China, Tiny bit in Vietnam [5]

Amur --- China, Russia [6]

Mekong --- China, Myanmar [7], Laos [8], Thailand [9], Cambodia [10], Vietnam [11]

Nile --- Egypt [12], Sudan [13], South Sudan [14], Ethiopia [15], Uganda [16], Congo [17], Kenya [18], Tanzania [19], Rwanda [20], Burundi [21]

Niger --- Benin [22], Guinea [23], Mali [24], Niger [25], Nigeria [26]

So 26 countries, with China clearly the worst.

However the majority of the plastic coming out of these countries is because of goods destined for western countries. Import tax based on Oceanic plastic emissions, with money used to clean up oceans, is the solution. This funds ocean cleanup, encourages better disposal, and puts the cost on the person driving it (the consumer)

Like CO2, plastic in the ocean is an externality that the world pays for, but doesn't benefit from.