A walrus which took itself ashore a number of times in Southeastern Finland in recent days, died while being transported to Helsinki's Korkeasaari Wildlife Hospital, the zoo tweeted late on Tuesday night.
The combination of the animal's weakened state and the ordeal involved in its examination and transport were too much for it, according to the zoo.
The walrus cow's condition began to deteriorate during Tuesday after the animal returned to land in the town of Kotka that morning.
It was anaesthetised at around 7pm for examination purposes, and then was successfully loaded into a wildlife transport vehicle at around 10pm.
The process of moving the animal to the transport vehicle took several hours.
The walrus's condition became increasingly poor over the course of the day, according to Korkeasaari Zoo's Director of Animal Care and Conservation, Nina Trontti.
"The animal was already in bad condition during the day, very quiet, not moving much and breathing quite heavily. Anaesthetising animals always carries a risk, but we wanted to try to help the animal," she told Yle TV1's breakfast programme on Wednesday.
Korkeasaari Wildlife Hospital is Finland's largest treatment facility for injured and orphaned wild animals.
The first reports of walrus sightings in Finland began last week in the seaside town of Hamina.
On Sunday, after having taken itself back to the sea, the marine mammal became entangled in a fisherman's net.
Following its release from that ordeal, the walrus appeared in Kotka on Tuesday, 150m from the river's edge, having clambered onto residential land. However, that evening, experts made the decision to transport the ill animal to the zoo for care.
Finnish law states that wild animals in distress need to be helped, with alternatives including transporting them to the care of an expert or euthanization.
Trontti noted that the zoo has received many questions from the public about why the walrus was not provided with help earlier, by giving it food and water, for example.
"I hope that people understand because the situation was new for everyone. We tried in the best possible way to help the animal," she explained, noting that the walrus swam off on its own after it first visited the Hamina riverbank last week.
"It would have been difficult to capture it at that stage," Trontti said.
There are no plans to organise a memorial service for the deceased walrus, but the animal carcass is headed to a pathologist for examination.
The aim is to determine whether its death was caused by its poor physical condition or other factors.
According to experts, the walrus likely swam around the Baltic Sea for some time, a region devoid of the nutrition that the animal requires. Among other things, walruses eat large quantities of blue mussels.