Irrigators that take water from the Opihi River are asked to help restore dam levels by reducing water consumption.
A lack of rain during the winter has caused concern about the level of the Opuha Dam in South Canterbury.
The Canterbury Regional Council requires the company that operates the dam to maintain a minimum current in the river of 5.2 cubic meters per second when it is more than 375 meters.
It is now at about 390 meters.
Although there are no actual irrigation restrictions, water permit holders are asked to reduce their water consumption to 75 percent of what their permission permits.
The Opuha Environmental Flow Release Advisory Group supervises the lake level.
The chairman Judy Blakemore said, while it was early in the irrigation season to impose water restrictions, a call for a modified two-week use was a precaution.
"The meter on the Opuha Dam has registered only 42.5 mm of rain since 1 June.
"Unfortunately, the rain we had experienced earlier this week did not make sense for the river basin and therefore we could not soften our concerns."
The capacity of the lake, inflow of lakes and snow packs are all important for the available water level for river flows and irrigation during a season.
All three were worried, Blakemore said.
Opuha Water Limited CEO Andrew Mockford said the forecasts were not good in the short and medium term.
"We do not see any significant rain on the horizon that will significantly change the circumstances."
Mrs Blakemore said that the drought in 2014 and 2015 illustrated the need for early intervention.
"We want to do everything we can to ensure that the 2018-19-19 season is no repeat of 2014-15 with empty lake, very low river flows and a stop for all irrigation."