The SOMLIT-Like -Lanvéoc time series data characterize the hydrology of the Bay of Brest, at 48°17'39"N - 04°27'09"W location. The Bay of Brest is a semi-enclosed, macro-tidal, marine ecosystem of 180 km², connected to the Iroise Sea by a narrow and deep strait of 2 km width, and 40 m depth max. It is under the influence of the Aulne river, representing 70% of the total river discharge. Fortnightly measurements have been undertaken since January 2019 by the IUEM/UBO/CNRS-LEMAR to detect the long-term evolution of hydrology in the land-sea continuum including natural and anthropogenic forcings. The data from the Lanvéoc station are collected according to protocols established by the French monitoring network SOMLIT (https://www.somlit.fr/), accredited by the CNRS as a national Earth Science Observatory (ILICO, https://www.ir-ilico.fr). The Lanvéoc station is upstream of the SOMLIT-Portzic observatory station (10.17882/91173). At the time of writing, the process of requesting SOMLIT accreditation for Lanvéoc station is underway. SOMLIT-Like-Lanvéoc samples are collected at 1m depth of a 10 m water column, at high neap tide (7m tidal range), near slack water. Samples collected are analysed for more than 20 core parameters: Sea Surface Temperature (SST), Sea Surface Salinity (SSS), dissolved oxygen (O₂), pH, ammonia, nitrates, nitrites, phosphates, silicates, suspended matter, particulate organic carbone, particulate organic nitrogen, chlorophyll a, delta15N, delta13C; pico- and nano- plankton; CTD-PAR-profile. The microphytoplankton is simultaneously identified in accordance with the national PHYTOBS-network’s (https://www.phytobs.fr/) protocols. Complementary parameters are also measured for specific research studies: biogenic silica  at 1m depth and the microphytobenthos and high frequency CTDO₂Fluo-measurements at sediment-water interface. The SOMLIT-Like-Lanvéoc time series data are collected in compliance with the SOMLIT network quality management system, in line with the kSO/IEC 17025:2017 standard: “General requirements for the competence of testing and calibration laboratories”. Further information on standard operating procedures for sample collection and data acquisition are available at: https://www.somlit.fr/parametres-et-protocoles. For more information on the quality flagging scheme: https://www.somlit.fr/codes-qualite/.