SAN DIEGO (CBSLA.com) — Federal authorities arrested suspects in two separate attempts this week to illegally enter the U.S. by jet ski near Southern California beaches, according to officials.

U.S. Border Patrol agents were alerted at about 5 a.m. Thursday by the Joint Harbor Operations Center (JHOC) and “a concerned citizen’s phone call” about a suspicious jet ski headed northbound from Mexico along the coastline in Imperial Beach, about 1 mile north of the U.S.-Mexico border, according to U.S. Customs and Border Protection (CBP).

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After being alerted that a person had been dropped off near Imperial Beach Boulevard, agents responded to the scene and discovered a 32-year-old Mexican national man hiding among the rocks on the beach, authorities said.

Agents determined he had illegally entered the U.S. and place him under arrested, according to CBP. He was transported to a local Border Patrol station for processing.

Two Mexican nationals were also arrested earlier this week near a Southern California Navy training facility after they entered the U.S. illegally by jet ski, authorities said.

On Sunday, San Diego Sector Border Patrol agents at the Joint Harbor Operations Center (JHOC) observed two jet skis heading towards the shoreline near the Naval Amphibious Base in Coronado around 8:45 p.m., according to CBP.

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Agents patrolling the area responded to a beach near the Navy SEAL team training facility and found a 34-year-old man and a 19-year-old woman in wet suits covered in sand, authorities said.

An immigration inspection revealed that unidentified suspects were illegally present in the U.S., according to CBP.

They were placed under arrest by Border Patrol agents and transported for processing, authorities said.

Since 2010, Border Patrol agents have made hundreds of arrests along the roughly 400-square-mile ocean expanse that stretches from the shores of Tijuana, Mexico, to suburban Los Angeles.

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Anyone in Southern California who has information about maritime smuggling or suspicious activity along the coast of California was asked to call 911 or 1-800-854-9834.