This multi-decadal time series initially contains water current and temperature data from a single, near bottom instrument. A second, shallower instrument recording the same parameters was subsequently added after several years of successful operation. Conductivity data are similarly integrated into the time series after a further period of operation. The data are typically at hourly resolution. The mooring is situated in the Tiree Passage, between the Isles of Mull and Coll, off the west coast of Scotland. The specific site chosen was where the passage is at its narrowest (10 km), mid-way between the coasts of the two Isles. The mooring site is in water depths of approximately 45 m. Mooring activity began in June 1981 and consisted of a single RCM current meter placed 11 m above the seabed. The mooring design was modified to incorporate a second RCM current meter at 22 m above the seabed from November 1987. Aanderaa conductivity sensors were added at the two depths in 1993, with MicroCAT conductivity sensors being incorporated in 2002. There are some gaps in the record, most noticeably between January 2000 and May 2002, a period when the observations were temporarily suspended. Fishing damage has generated smaller gaps in the data set over the years. This region was chosen as a site for long term monitoring after radiocaesium studies showed that the major part of the water carried northwards from the North Channel in the Scottish coastal current passes between Mull and Coll. The mooring provides data for comparison with tracer studies and for an examination of the roles of wind forcing and buoyancy contributions to the coastal current. Tiree Passage mooring work is led by Colin Griffiths at the Scottish Association for Marine Science (SAMS).