Riverside County officials on Thursday unveiled a possible $400-million remedy for some of what ails the shrinking Salton Sea: record-high salinity levels, die-offs of fish, fewer birds and an immense “bathtub ring” of smelly playa prone to toxic dust storms. The so-called North Lake Vision proposed by Riverside County Supervisor Manuel Perez calls for creation of an in-lake barrier, or dam, on the north end of the sea that would be filled with enhanced flows from the White Water River to create what he described as “a 4,200-acre healthy lake within a much larger not-so-healthy one.”