Bay of Plenty cows will be on the roads this weekend as sharemilkers move stock on what's known as gypsy day.
Farmers relocate themselves and their stock in time for the new season, which begins on June 1.
That puts a lot of animals on the road or in stock trucks - and potentially a lot of effluent on the road, even if farmers only move a short distance, according to the Bay of Plenty Regional Council.
This year's moving day coincides with Queen's Birthday weekend holiday on Monday, which means there may be more than the usual traffic on roads.
Bay of Plenty Regional Council's Pollution Prevention Manager Nick Zaman said most farmers and carriers managed gypsy day well, but there was still a risk of effluent ending up on roads, which could reach waterways.