New Zealand could face power shortages this winter unless the hydro lakes get a significant boost soon.
Hydrologist David Stewart says the South Island lakes were spilling over just three months ago, but water levels have been dropping steadily since.
He says lakes Te Anau, Manapouri, Wanaka and Wakatipu are especially low.
"The lakes over there probably need two or three decent storms with more than 100 millimetres at a time.
"That would give them a decent sort of a boost, it would bring them up to more normal levels for this time of the year.''
Mr Stewart says Lake Pukaki needs even more rain, as its levels have already dropped 5.5 metres below their peak.