SAN JOSE, Calif. — A toxic red tide has returned to San Francisco Bay, raising fears of a reprise of last summer’s unusually large fish die-off. Experts report that swimming algae was detected last weekend in rust-colored water samples from Emeryville, the Berkeley Marina, Albany and Marin County’s Richardson Bay and Muir Beach. While no fish deaths have yet been reported, authorities are advising against people or pets entering the water and are closely monitoring the bloom. Last summer’s incident was alarmingly deadly, killing thousands of fish and other marine creatures, from tiny yellowfin...