The sediment build-up at the Butcher's Drive was a natural occurrence, and was getting worse, Colliers International property manager Rose Quirk, acting as agent for Land and Information New Zealand (Linz), said at last week's council community services committee meeting.
However, because the build-up could not be stopped, Linz would not be doing any more work to remove the sediment, Ms Quirk said.
She said the sediment build-up had made conditions dangerous where boats were put into the lake.
Some councillors asked if the boat ramp should be decommissioned if it could not be used or should not be used because of safety issues.
"It's a boat ramp - you expect to be able to launch your boat," Cr Shirley Calvert said.
Lake Dunstan marine patrol, education and enforcement officer Shayne Hitchcock said there had been a "tipping point" with the boat ramp last summer in terms of user numbers. The area usually had very high usage, but numbers of boat users there last summer were down on the previous summer. This might be because of the shallow areas around the boat ramp, Mr Hitchcock said.
He suggested a publicity and education campaign, so people were aware of the issues at the boat ramp.
Cr Stephen Jeffery also suggested asking Contact Energy if additional warning signs could be installed at the site.
When contacted after the council meeting, Linz group manager land and property Stephanie Forrest said Linz was discussing the sediment issue with Contact.
"We need to investigate this in more detail to understand what further action might be required, including the need for any signage, public information and education."
