RENO, Nev. (AP) — The clarity of Lake Tahoe's cobalt blue water improved last year from its worst level in a half-century after weather and runoff returned to more normal conditions at the alpine lake straddling the California-Nevada line. A dinner plate-sized disc used to measure clarity was visible at an average depth of 70.9 feet (21.6 meters) in 2018, scientists at the University of California, Davis, Tahoe Environmental Research Center said Thursday. That's an improvement of 10.5 feet (3.2 meters) from 2017 when a winter with unusually heavy snow followed years of drought, sending sediment into the scenic lake known for its pine tree-lined beaches and ski resorts.