WaterNSW is advising customers supplied from Brogo Dam that general security irrigation availability will cease from 6am on Saturday, January 11 as a result of temporary rule changes announced on Wednesday.

The restrictions will enable town water needs to be met over the summer and autumn periods, the department said.

WaterNSW met with customers in the region in early December to advise that severe drought conditions and the corresponding impact on inflows had reduced Brogo Dam storage from 100 per cent in May 2019 to 13 per cent in January 2020.

In February last year, apart from Lake Cargelligo and Doctors Point on the Murray, Brogo Dam was the only dam run by Water NSW in the state with a rising water level, and the only dam that was full.

The state government said its priority is to retain at least 1200 megalitres of water in storage to supply town water for Bermagui and other local users including stock and domestic supply.

"Unregulated and groundwater users in the mid-Bega River sands water source are also reminded that restrictions on take of water apply, once the level at monitoring bore GW039001 falls below 5.5m AHD," WaterNSW said this week.

"Access is only allowed to the low flow class - between 5.5m and 4.5m AHD - for those licences specifically accredited."

Brogo Dam is the main source of water for the towns along the Bega and Brogo rivers, which rely on the Brogo-Bermagui Water Supply System, besides limited groundwater access.

To secure critical water supplies, access to all water remaining in general security accounts will be prohibited until there is sufficient resource recovery via inflows into Brogo Dam. The order will be in place until June 30.

Under the terms of the temporary changes low rate releases of 5-6 megalitres per day (ML/d) or less will be made for town supply, which will also be accessible by domestic and stock licences and basic landholder rights.