Another 25 on Lake Wendouree's eastern side are also unlikely to survive, leading into another dry summer.

City of Ballarat contractors began removing the trees this week, which include four sequoia trees, a poplar, a tulip tree and a tortured willow.

The works are expected to continue into next week.

The council said it needed a planning permit to remove the trees with the area covered by a heritage overlay.

It also received approval from the Friends of the Gardens and the Lake Wendouree and Gardens Special Committee.

Replacement trees will be planted next autumn when the weather conditions are appropriate.

City of Ballarat chief executive officer Anthony Schinck said it was disappointing the trees had to be removed, with some more than a century old.

In June this year, Ballarat's sequoias were said to be showing positive signs after being threatened by the fungal disease cypress canker two years ago.

Four of the 24 original trees in the gardens' avenue were under serious threat, with the other 20 showing signs of recovery.

Council's watering program in Sturt St has also resumed, with 41 new trees planted between Doveton and Pleasant streets.