Wisconsin authorities investigating fatal dog and wildlife poisonings near the border with Michigan’s Upper Peninsula say the death of a 3-year-old German shepherd earlier this month is the latest believed linked to the rash of cases.

The dog was on a leash and being walked by its owners on public land in northern Forest County on April 1 when it died suddenly, according to the Wisconsin Department of Natural Resources. While lab tests are still pending, a fast-acting toxin is suspected, similar to the poison known to have killed several domestic dogs and wildlife within a three-county area of northern Wisconsin since December of 2018.

The German shepherd’s owners told authorities they saw some dead ravens in the area where they had been walking their dog. Authorities are encouraging pet owners in Forest, Marinette and Florence counties to be on guard.

Forest County, where the shepherd died, is just across the border from Michigan’s Iron River area.

“The public is advised to use dog leashes and watch for signs - such as dead wildlife - that poison may be in the area,” Wisconsin DNR Lt. Bryan Harrenstein said.

Before the shepherd died, the last two casualties linked to the poisonings were a pair of beagles who died in March.

In the previous deaths, lab tests have confirmed what authorities have called a “dangerous toxic substance.” Investigators believe it’s being mixed with meat and left out for animals to find.

In addition to several pet dogs, there have been wildlife deaths linked to poisonings in that area. These have included raptors, coyotes, weasels, raccoons and wolves, the DNR said.

Any tips can be called in or texted to 1-800-TIP-WDNR, or 1-800-847-9367.

The U.S. Fish and Wildlife Service, which is also investigating the poisonings, is offering a $1,000 reward for information leading to an arrest and charges in the cases.