Overnight into Wednesday, Michigan City Parks and Recreation said two animals died due to "separate medical events."
A wolf died from natural causes and a lemur died due to lung failure.
Officials said after the wolf died there was an "incident" between other wolves and animal care staff.
A spokesperson for the department said "all involved are stable."
The zoo opened to the public on Wednesday. However, the main wolf exhibit will be closed while staff "assess the situation."
No other information was available.