Community representatives, environmentalists and concerned landowners are being urged to attend the "Win-Win Sydney Catchment Workshop", which is expected to start at 10am and conclude at 4pm.

The Sydney catchment is arguably the most valuable in Australia as it provides clean drinking water to four million people - 70 per cent of the population in NSW - yet workshop convenor Mike Thompson believes its management is under threat of falling victim to a political nonsense.

Mr Thompson, a member of the Friends of Sydney Catchment who lives at Mittagong, is concerned that two-thirds of the area currently controlled by the Sydney Catchment Authority is also to fall within the boundaries of the Hawkesbury-Nepean CMA, which is to have about 15 staff supported by the State Department of Infrastructure, Planning and Natural Resources (DIPNR).

He told the News that while the formation of CMAs provided a great opportunity for integrated natural resource management throughout NSW, there was a risk of duplication and confusion if two separate authorities were to make decisions and implement strategies for the one area.

"It hasn't been figured out how the two are going to work together," said Mr Thompson.

"And there is a danger that the Government will leave it in the 'too hard' basket."

Representatives from DIPNR, Sydney Catchment Authority and the NSW Farmers' Association are to be among speakers at the workshop.

A submission to government about how Sydney Catchment Authority should operate for the next five years - the deadline for which is Monday - will also be prepared.