Maori tribe Ngai Tahu fears waterways and wildlife will suffer if applications to irrigate another 16,000 hectares in Upper Waitaki are granted.
Thirty-two applicants have lodged 110 applications with the Canterbury Regional Council for new or renewed consents to irrigate the area, which would take the amount of irrigated land to 28,000 hectares.
Ngai Tahu told a panel of four independent commissioners on Monday that the area is a traditional food gathering place and is of great cultural importance.
It told commissioners it supports providing water supply security to landowners, but is worried the land could be converted to dairy.
It says dairy conversions have largely led to environmental problems, including poor water quality in rivers and lakes, affecting fish life.
Ngai Tahu told the hearing the applicants have provided insufficient information to ease the tribe's fears, saying many dairy farmers fail to comply with consent conditions.
Three of those seeking consent are also behind plans for 16 new dairy farms in Upper Waitaki, where thousands of cows would be kept indoors.
A further hearing of effluent consent applications from the three companies, Five Rivers, Williamson Holdings and Southdown Holdings is due to begin in March.
Because of debate over the environmental impact of the planned intensive dairy farms, Environment Minister Nick Smith is considering whether to "call in" the consents, which would put the decision in Government hands.