Description of the data and files: The data was created in 2018 and opened in 2021. Dataset is an Excel table file MpKallavesiMIF_rawdata.xlsx. The first tab “Sampling” contains coordinates, where the samples were collected and volumes of water per samples. The second tab “Manta FTIR Results” contains light microscopy and FTIR microscopy measurement data from all particles found from the Manta net samples. Similarly, the third tab “Pump FTIR results” contains light microscopy and FTIR microscopy measurement data for particles from pumped samples. The fourth tab “Controls” contains light microscopy and FTIR microscopy measurement data for control samples. The fifth tab “Materials” contains statistics for the shapes (fibers/fragments) and polymer types of the microplastics. Please see the related publication for more details about the methods and results. Creation and processing of the data: Data is created by examining the appearance and chemical composition of the suspected microplastic particles by light microscopy and FTIR microscopy. Correlation coefficients have been calculated between the measured FTIR spectra and a reference library of plastics. In addition to the raw data, the file contains statistics calculated from the raw numbers. Purpose and use of the data: Data is published under Creative Commons CC-BY 4.0 license. Data may be useful for comparisons between datasets and meta-analyses of microplastic concentrations in various environments.