Water level data recorded in the Oir watershed are acquired in a sector at the outlet of the Ruisseau de la Roche (tributary of the Oir) for the Environmental Research Observatory (ERO) on Diadromous Fish in Coastal rivers (DiaPFC). The DiaPFC ERO is a research infrastructure focused on studying the evolution of diadromous fish populations under the influence of environmental and anthropogenic changes (mainly agriculture and climate). The Oir is a tributary of the Sélune, a coastal river that flows into the Bay of Mont-Saint-Michel. The river stretches 13.5 km from west to east, draining a catchment area of 85.4 km². Average flow is 1.09 m3/s. Agriculture, particularly livestock farming, is the main human activity in this watershed. The Oir is colonized by several species of migratory fish: Atlantic salmon, European eel, sea and river lamprey, sea trout, etc. Other series of data are recorded for this same sector: Water temperature : https://doi.org/10.15454/YFY4AQ Rainfall : https://doi.org/10.57745/V9POHR. Physico-chemistry (conductivity, pH, nitrate, phosphorus, etc. ) : https://doi.org/10.15454/SGO7EU Trout, eel and salmon populations are monitored by electrofishing, and individual pit-tag monitoring is carried out on these species. Water levels are recorded at the following geographical position: latitude: 48.63824; longitude: -1.188991. The sensor is placed in a channel with a known trapezoidal cross-section for flow calculation. Data have been recorded since 25/10/2010. Equipment used : from 10/25/2010 to 01/20/2016: HOBO datalogger U20 WATER LEVEL probe (10-minute frequency) from 20/01/2016 to 23/06/2023: OTT PLS probe (10-minute frequency)