The River Lee (Irish: An Laoi) is a river in Ireland. It rises in the Shehy Mountains on the western border of County Cork and flows eastwards through Cork, where it splits in two for a short distance, creating an island on which Cork's city centre is built, then passes through Cork Harbour on the south coast, one of the largest natural harbours in the world, to empty into the Celtic Sea. The catchment area of the River Lee is 1,253 km². The long-term average flow rate of the River Lee is 40.4 cubic metres per second (m³/s).

A hydro-electric scheme was built on the river, upstream from Cork City, and this part of the river now contains the Carrigadrohid and Inniscarra reservoirs. The river is crossed by 42 bridges, 29 of which are in Cork City, and one tunnel. The river also provides an 8-kilometre (5.0 mi) stretch of salmon fishing.^{[citation needed]}

Ptolemy's Geography (2nd century AD) described a river called Δαβρωνα (Dabrona) or Λαβρωνα (Labrona), which is sometimes considered to refer to the River Lee. Though unconfirmed, the Irish name for the river, Laoi, may derive from Corca Luighe, which in turn derives from 'Luighe', the son of a quasi-mythical Milesian noble.

There is also the Λουρ (Lour), a separate river which passes through Tralee.

The River Lee has its source in the Shehy Mountains near Gougane Barra, where there is a forest park, chapel, hotel, and shop.

The Lee flows from the lake of Gougane Barra as a fast-paced torrent, but by the town of Ballingeary it eases and flows into Lough Allua. Departing the lough, running east, it again becomes a rapid flow before running into The Gearagh, and Carrigadrohid feeder reservoirs, and then into the large Inniscarra reservoir created by Inniscarra Dam. Moving on, it flows down from the dam, in normal conditions a gentle river until it comes to Ballincollig Weir in Ballincollig Park; here it is dangerous to swimmers when in high water. The Lee then flows into the city under Inniscarra Bridge and flows parallel to the Carrigrohane road. Along this section gauges monitor the water levels from the Inniscarra Dam. The river flows over the Lee weir and then is split into the north and south channels at a sluice (it historically occupied the city area as a maze of channels). This area is popular for recreation, kayaking and fishing. The two channels join again at the Cork docks and enter the extensive estuary and harbour, south of Glanmire, passing either side of Great Island (Cobh lies on the south coast) to fill the outer harbour, and reaching the open sea between Whitegate and Crosshaven.

High tributaries include the Owenagariff, the Bunsheelin, the Paudeen and the Garrifowa.

Tributaries joining below Lough Allua and Inchigeela include the River Toon, the extensive Sullane River system, from near Ballyvourney (tributaries include the Douglas, Finnow, Foherish and Laney or Laine Rivers) via Macroom, the smaller Buinea and Glashagariff Rivers, and the River Dripsey and its tributaries the Rylane and the Delaghinagh.