Commercial citrus growers have dwindled over the past few decades in south Louisiana, where farmers have had to battle hurricanes, flooding, invasive insects, freezes and drought to keep their groves alive. The latest hurdle comes from a slow-moving threat — a mass influx of salt water from the Gulf of Mexico that is creeping up the drought-stricken Mississippi River. Not only is the saltwater intrusion threatening drinking water supplies for communities, but it can also kill citrus seedlings.