Facing the bans are parts of the Ngaruroro, Waipawa and Tukituki rivers and, unless there's rain, more than 200 water rights holders will be hit.
"This is an important time of year for Hawke's Bay's cropping farmers, so as you can imagine this is a very stressful situation for all farmers," he said.
The warnings came as temperatures in parts of the Bay yesterday passed the 30C mark again, although generally 3-4C below Thursday's readings.
The highest on recognised websites was a maximum of 32.2C in Wairoa, compared with 35.2C the previous day, when another website reported a personal weather station (PWS) high at Nuhaka of 37.7C.
Temperatures were cooling by late afternoon, well below those of the same time the previous day, when temperatures peaked at about 4.30pm.