Microplastics sampled downstream from a total of eight rivers were analysed as the first attempt to determine microplastic composition in rivers and load to Mersin Bay, in the north-eastern Mediterranean Sea. With a share of 83.5%, fibres were the dominant category from all samples. Basic characteristics (form, colour, average size, polymer) of microplastics from these rivers were similar to those reported from the marine environment in Mersin bay. The overall average number of microplastics calculated for the eight rivers was determined as 293 +/- 59 particles/m(3) equalling a load of 1200 billion items (mainly from the Goksu River) discharged annually to the northeastern Mediterranean. This value equivalent to twice the total stock of microplastics within the water column in Mersin Bay, demonstrates that rivers are a primary source of microplastics pollution for the coastal seas.