Regional councils and the police are urging farmers and stock transport companies to be vigilant about effluent management as people prepare to pack up and move on to new milking contracts.
Over the next month or so, thousands of cows will be transported between farms as dairy farmers take up new contracts - usually on June 1, or what is known as Gypsy Day.
Otago Regional Council director of environmental monitoring and operations Jeff Donaldson said cattle should be kept off pasture for about 12 hours before they go on a truck, so their stomachs were empty and there was less chance effluent would end up on roads.
"It is a requirement before they're transported that they stand them for a minimum of 12 hours so the cattle can empty out.
"It makes the animals much easier to transport, it keeps them cleaner if they're not standing or lying in effluent, it's also much better for the roads.
"Approved transport operators, most of them have [effluent] storage facilities on their trucks but it's the smaller operators - hay carting contractors and such like - that start carting stock at this time of year and they don't have the capacity on their trucks so the police will certainly be looking for those who don't have [effluent] storage facilities available," he said.
Waikato Regional Council's senior transport advisor, Isy Kennedy, said effluent on the road was a farmer's responsibility.
"Farmers have got to stand their stock, they just can't run them in off green feed. The fuller the belly the more likely there's going to be a heck of a lot more effluent...when the cows get rounded up they get very stressed ...if they've got a fully belly they're very unstable. Not all farmers have a stand off paddock but if they can just stand them where there's very little green feed."
In the early 1992 a motorcyclist was killed in south Waikato, near Putaruru, when his bike slipped on effluent.
Ms Kennedy said there was legislation that could lead to people being prosecuted for a failing to manage effluent, but she believed it needed to be tightened up.
"There's a lot of legislation that sort of alludes to effluent on the roads, sometimes it's not to referred to as that, it's called an unsecure load, but it's very very difficult to nail a truck driver if a person doesn't get their registration number, the name of the truck and the location."