OAKLAND — The opening of a new gondola and restaurant at the Oakland Zoo — the first phase of the zoo’s $70 million California Trail expansion — has been delayed.

The gondola and cafe were slated to open Monday, but the zoo is apparently trying to fix a problem in the restaurant before opening.

“We are working with the City of Oakland to resolve an issue with the water-pressure system in our new restaurant, and will not be able to open our gondola and The Landing Cafe at California Trail on Monday as planned,” the zoo wrote in a Facebook post on Sunday.

On Monday, a Facebook post from the zoo said it was still working on the water-pressure system and said the system will be re-tested by the city Thursday.

Once they are ready, the eight-person electric gondolas will take passengers to the visitor center and a new floor-to-ceiling glass-walled restaurant, The Landing Cafe, that has views of San Francisco Bay.

The entire California Trail expansion will double the size of the complex to about 100 acres. Slated to open next summer, it will allow visitors to get up-close views of native California species. The $81 million redevelopment effort included a new veterinary hospital finished in 2012, the Oakland Zoo Biodiversity Center opened in 2013 and the Condor Recovery Center opened in 2014.

Plans for this part of the project have been in the works for more than two decades, and construction started in 2015.

Staff writer Erin Baldassari contributed to this report.