Marin County water agencies are expressing cautious optimism about a new proposal to transfer ownership of a controversial hydropower plant that affects one of the county’s main water suppliers. The proposal centers on the Potter Valley Project, a 110-year-old hydropower plant in Mendocino County that is operated by Pacific Gas & Electric Co. Water diverted by the plant feeds into the Russian River watershed, which is a key part of Marin’s water portfolio. After PG&E announced its intention to surrender and decommission the power facility in 2019, there has been a question of whether water diversions to the Russian River would continue. The new proposal submitted this month by Sonoma Water, the Mendocino County Inland Water and Power Commission and the Round Valley Indian Tribes would transfer parts of the facility to a new entity that would continue Russian River water diversions.