This dataset describes the quantity and morphology of microplastics in water, sediment, fish, and mussel samples from the Delaware River and select tributaries, including portions of the Upper Delaware Scenic & Recreational River, Middle Delaware National Scenic River, Delaware Water Gap National Recreation Area, and Lower Delaware Scenic & Recreational River. Water and sediment samples were collected at nine locations, from Callicoon, New York, at the upstream end, to Burlington, New Jersey, at the downstream end. Smallmouth bass (Micropterus dolomieu), white sucker (Catostomus commersonii), and eastern elliptio (Elliptio complanata) were sampled at a subset of locations to assess biological uptake of microplastics. Sampling and analysis methods are described in the Processing Steps section of the metadata. Samples were collected July 2018 - March 2019.