When Gov. Gavin Newsom downsized the Delta tunnels water project last year, the idea was to save money and try to appease at least some of the project’s critics.

Yet the project remains controversial — and still figures to be costly.

After months of relative quiet, Newsom’s administration released a preliminary cost estimate for the scaled-back project Friday: $15.9 billion for a single tunnel running beneath the estuary just south of Sacramento.