A nonprofit that rates water quality at West Coast beaches just gave Marin a near-perfect score, based on weekly samples collected seasonally at sites across the county last year. Part of the beach monitoring program, the county’s Environmental Health Services division gathered the data between April and October from 23 spots, including Stinson Beach, Muir Beach, Bolinas Beach, and seven beaches on Tomales Bay. Nineteen locations received A-plus wet-weather ratings and the remaining four were…