Marin County water district officials expressed encouragement after an early agreement was reached that seeks to end longstanding conflicts of a major regional water supply 100 miles to the north. The agreement centers around the relicensing of the Potter Valley Project hydropower plant in Mendocino County, which holds a supply of water that affects fish, farmers and communities stretching from Marin to Humboldt counties. Sonoma Water, one of the main suppliers to Marin’s two water districts, draws water supplied by the power plant’s reservoirs.