Lake Argyle is an artificial lake in the Wairau valley, constructed as a storage reservoir for the Branch hydro-electric scheme. The hydro scheme as originally constructed belonged to Marlborough Electric Power Board, however under electricity reforms introduced by Max Bradford, energy companies were not permitted to both own distribution networks and generation, and MEPB elected to sell its generating assets to Trustpower, who are the current owner of the lake.
Lake Argyle is constructed from rock and earth embankments on the western and northern sides while a hillside provides natural containment on the eastern side. The lake is fed by water diverted from the Branch River, which enters a concrete feed structure designed to prevent rocks and sediment entering the lake before entering a series of canals. Water exits through into a small powerhouse and then into a canal that feeds water to a second power house near the Wairau River which generates the majority of the electricity produced by the hydroelectric system.
The lake is well stocked with trout and a concrete boat ramp is provided at the south east end of the lake. Speed restrictions of 5 knots are imposed by government regulations.