Production at the £140m Glendoe scheme, near Fort Augustus, stopped in August 2009 when rocks fell into a tunnel carrying water from a hilltop reservoir to the turbine.
It had been officially opened by the Queen in June.
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Operator Scottish and Southern Energy (SSE) announced it hoped to start refilling the reservoir this winter in time to start generation again next year.
Two new tunnels were created to bypass the blocked one.
SSE said: "Work on the restoration of electricity generation at the Glendoe hydro electric scheme is continuing to progress well and investment is being made to ensure it is carried out to a very high design specification.
"Repair of the tailrace has also commenced. This means the process of refilling the reservoir should begin around the end of this winter and electricity generation should resume in the first half of 2012."
(JG/BMcC)
