MILWAUKEE (CBS 58) -- The Milwaukee County Zoo is preparing to say goodbye to an iconic part of its history.

This year, the North Shore Bank Safari Train's No. 1916 and No. 1924 steam locomotives will leave the station for the last time. 

The zoo says the engines will be transferred to the Riverside & Great Northern Preservation Society in the Wisconsin Dells, with the No. 1916 engine slated to depart on April 1, followed by the No. 1924 engine on Oct. 31. 

According to the zoo, the sale of the steam engines supports their mission of conservation and sustainability.

They say the train will continue to operate as usual with their diesel engines, and the zoo plans to acquire two new, custom-built diesel engines for future use. 

In an announcement Thursday, the zoo wrote, in part; 

"Since 1992, the Zoo’s four locomotives — two steam and two diesel — have powered the Train to carry more than 400,000 guests annually throughout our parkland. We honor the countless memories that the steam engines have helped create over the years and look back fondly at the legacy they leave behind. And yet, we look forward, to a brighter and more sustainable future as the Zoo embraces the next generation of diesel locomotives to come."

The zoo says they'll announce a limited run of the No. 1924 steam locomotive for guests to enjoy later this year, before its transfer.