Loch Tarsan is a freshwater loch and impounding reservoir located 13 kilometres northwest of Dunoon, Argyll and Bute, Scotland.

It supplies water to the Striven Hydro-Electric Scheme (also known as the Cowal Hydro-Electric Power Scheme).

The larger of the two dams is 17.6 metres high and was completed in 1953.

The water that is collected in the loch is piped to the hydro-electric generating station, located at Ardtaraig, at the head of Loch Striven.

[2] The B836 road passes the loch.