Julian Aitken regularly tests the water underground and downstream from his feedlot.
"We are having no impact, in fact nitrogen levels are lower downstream than they are upstream," he said.
It has been on the former Waipawa River riverbed since the 1970s, where beef cattle are fed a variety of foods for three months over winter.
They were recently released to enjoy the spring flush.
"It is far cheaper to put them onto grass than to feed them supplementary feed.
"Supplementary feeding is a very normal farming practice, but obviously it is creating quite an issue now. With drones now there is nowhere to hide, which is good.
"We are trying to use best practice and look after the environment like everyone else."
What is not best practice is long-term supplementary feeding on one or two muddy paddocks.
"If you feed out on soil - farmland - then you can get pugging, which damages the soil. Plus you can get erosion of the soil which can go into a stream and is the main reason phosphates get into the stream, so it is far better to have it on a hard surface."