Warning signs remain posted at Waimea Bay today after an aggressive shark was spotted offshore.

At about 9:45 a.m., a 5- to 6-foot shark was spotted about 30 yards offshore, according to city Emergency Medical Services spokeswoman Shayne Enright. Lifeguards observed the shark thrashing in the water and chasing schools of fish, she said.

Lifeguards are urging beachgoers to stay out of the water.

Sharks have been seen frequently at Waimea for the past week. On Monday, multiple aggressive sharks were observed likely feeding on fish about five years from the shore. Last Thursday, a 6- to 8-foot shark was observed feeding on fish about 30 yards offshore.

Researcher Carl Meyer of the University of Hawaii’s Institute of Marine Biology said the sharks are likely drawn to schools of juvenile akule (halalu) that typically spawn in bays and harbors in mid-t0-late September.

Large schools of juvenile fish been observed at Waimea Bay and other coastal areas in recent weeks, according to Meyer.

“The schools of fish are probably attracting sharks close to the shoreline where they are easier to spot,” he said. “The shark activity will taper off as the schools dwindle or disperse,” Meyer said Wednesday in an e-mail.