Marin water managers zero in on supply options

Reshaping the Nicasio Reservoir is the most efficient way to add to the water supply in Marin, county water managers said.

A new cost analysis presented to the Marin Municipal Water District board this month showed that the $5 million project would provide significant supply gains for a relatively low cost when compared to other proposals under consideration — many of them tagged with estimates exceeding hundreds of millions of dollars.

The Nicasio project would modify the reservoir’s...