The hearing Tuesday was part of the process for five farms looking to expand and greatly add to the county's cow population.
Opponents said the manure from those cows would hurt an already contaminated water supply.
"Increasing herd size is not going to fix the problem. It might help a few people to stay in business but it is not the answer for the majority," said Susan Marks, part of the Door County Environmental Council.
Farmers, however, said expansion comes with new technologies to improve the environment.
"I think the question is, are we bringing more cows in with practices of the past, or are there more cows with practices of the future?" said Don Niles, owner of Dairy Dreams Farm.
Residents have a week to submit comments to the DNR. Officials said this hearing is part of a typical application process, and based on information so far, there's no reason not to issue or reissue permits for these farms.