The Maine Warden Service is looking for the person who set an illegal gill net in the Magalloway River in northern Oxford County.
The use of a gill net in fresh water is illegal.
Mark Latti, spokesperson for the Maine Department of Inland Fisheries and Wildlife, said a few dead trout and other fish species were found entangled in the net.
"This net in its total length was 36 feet long and 9 feet deep, which is enough to put it across most rivers and streams," he said. "Once a fish gets caught in it, they die."
The Magalloway is a premier spot for brook trout.
"Brook trout are one of those special species of fish, and the damage that a net like this could do to a stream like that is very alarming," Latti added.
It's unclear how long the gill net has been set in the river, and whether, or how many fish, have been taken from it, Latti said.
Maine Operation Game Thief originally offered a $1,000 reward to those who can provide information leading to an arrest. Latti said a concerned citizen has offered to double the reward to $2,000.
