A yearlong study of Sag Harbor Bay has found its water quality to be good over all, but also has detected high nitrogen or bacteria levels at several trouble spots, among them Havens Beach. The level of fecal coliform bacteria in water emanating from a drainage ditch there was 100 times higher than the state's standard for safe shellfishing, and the level of enterococcus bacteria was 10 times higher than the standard for safe swimming.