A 15-foot boat carrying 21 suspected illegal immigrants from Mexico was spotted off a San Diego-area beach Tuesday and its occupants arrested, authorities said.

The boat was the third in the area to be intercepted by the Border Patrol in the past few days, the San Diego Union Tribune reported.

Border Patrol Agent Mark Endicott said the boat, spotted just before 5 a.m. Tuesday, was carrying 19 men and two women, all Mexican nationals. It was first spotted about a mile out and tracked to Beacon's Beach in Encinitas.

Eight people on an 18-foot Bayliner were taken into custody Saturday.

On Sunday, 13 people were taken from a 22-foot motorboat at a marina in Oceanside Harbor. Two men were accused of being human smugglers. Seven other men and four women came from either Mexico and Bolivia, authorities said.