Hundreds of red-breasted mergansers have been affected by a bird flu outbreak on Chicago's Lake Michigan shoreline, raising concerns for wildlife and pets.

A version of the H5N1 virus that has killed one person and severely sickened another has been detected in milk samples collected from Nevada dairy herds.

In an announcement, the zoo said the closure "is out of an abundance of caution meant to protect our avian population from HPAI, commonly known as Avian Influenza, after recent, suspicious bird deaths on the Chicago shores of Lake Michigan."

H5N1 bird flu — have been found along the shores of Lake Michigan in the Chicago area, prompting warnings from area health officials. (

Public health and natural resource managers in both Illinois and Wisconsin are looking at, but have not yet confirmed, if bird flu is responsible for dozens of bird deaths along lake Michigan. Reports started coming in after dozens of dead ducks washed up on lake beaches between Chicago and Milwaukee.

The outbreak started in December and has now spread from a few reports in the suburbs to hundreds in the city, along Lake Michigan, over the last week.