Southland Regional Council is considering enforcement action against dairy farmers and contractors whom it accuses of environmental vandalism.
It says a farmer at Mataura straightened a stream by cutting 80 metres of meanders so he could plough and cultivate the land more easily.
In another case, an Otautau farmer cultivated a large area of wetland on his property and another dammed an Orauea stream illegally to provide water for a new dairy farm.
None of the landowners had resource consents for the work.
Consents manager John Engel says work that was done without a consent may have to be reversed, resulting in a lot of extra cost to the individuals.
Mr Engel says contractors can also be liable for prosecution and they should check the resource consent before they start work to see if any conditions have been imposed.
He says the council may decide to impose fines of up to $1,000. If court action is taken, the individuals could face fines of up to $200,000.