Six of the nine planks on the roof of the structure protecting the outlet valve controls have been smashed by large rocks dropped over the dam wall and a gate on the dam has now been locked to keep out visitors.
The chairman of Last Chance Irrigation Company, Gavin Dann, said yesterday that if the valve itself had been damaged, the impact on the dam would have been serious.
Conroys Dam has been used to store water for irrigation since 1935.
‘‘Without this dam, there would be no orchards or vineyards around here,'' Mr Dann said.
The dam has become popular for walking, swimming, picnicking and fishing.
Mr Dann said it had also become popular with those wanting to go somewhere to drink alcohol and then ‘‘look for other forms of entertainment''.
The Department of Conservation has opened the Aldinga Conservation Area above the dam.
Doc visitor assets manager Anita Middlemiss said it was disappointing the action of a few thoughtless people had forced the closure of a much-used walkway.
Anyone with information about the vandalism, believed to have occurred between March 25 and April 3, is asked to tell the Alexandra police.
