A new restriction has been imposed on Murray-Darling basin water license-holders.

From today, trade from above the Barmah Choke in NSW to below the choke will be restricted, in an effort to protect downstream water supplies.

Trade downstream can only occur if upstream trades of the same or greater volume have been made.

The Murray-Darling Basin Authority says no limits have been placed on upstream trades, creating more opportunities for downstream trading through the choke.

“At the moment it’s very dry and the dry conditions are forecast to continue—that means we're probably heading into a period of high demand for water entitlements,” MDBA River Management executive director David Dreverman said.

“Furthermore, there are reasonable water allocations currently available and most water is stored in our major storages upstream of the choke, meaning there will be heavy demand on the channel.

“There’s also no ability to draw on water from the Menindee Lakes.

“So, to protect delivery of existing entitlements, it's necessary to re-instate the trade restriction.

“Water planning for summer is now relying on meeting downstream demands by drawing water from the Goulburn and Murrumbidgee rivers, and using the Mulwala Canal and its escapes to bypass the choke.”

The MDBA says some water is available to be called from the Goulburn and Murrumbidgee rivers as a result of earlier trades.

Mr Dreverman said the MDBA would continue to monitor the situation and if circumstances allowed, the restriction would be relaxed.