The performance of various standard algorithms for the retrieval of suspended particulate matter (SPM) from Sentinel-2 MSI and Landsat-8 OLI satellite data obtained in 2019 and 2021 is discussed. The study was conducted for the estuaries of 2 mountainous rivers originating in the Caucasus Mountains: The Sulak River flowing to the Caspian Sea and the Mzymta River flowing to the Black Sea. The rivers differ in the degree of flow control and the composition of terrigenous suspended matter carried to the sea. The main objective of the study was to compare SPM retrieval results of the C2RCC (Case 2 Regional Coast Color) processor and the ACOLITE (Atmospheric Correction for OLI †lite') algorithms Nechad 2009, Nechad 2015 and Dogliotti. The satellite data were verified against in situ measurements of turbidity and SPM performed synchronously with the satellite survey. Field measurements from a small boat were performed in April and May 2019, 2021 in the northeast Black Sea, in the mouth area of the Mzymta, and in May 2021 in the Sulak mouth area. The measuring instruments and methods included a turbidity sensor mounted on a CTD (conductivity / temperature / depth) probe, a portable turbidimeter, and water sampling for further laboratory analysis. It was established that for low SPM, 20-30 g/m3, performances of C2RCC and Nechad 2015 practically coincided and correlated well with the in situ data. For large SPM, over 300 g/m3, the best performance was demonstrated by Dogliotti, an algorithm designed especially for extreme SPM values.