Twelve alleged members of the criminal gang Los Zetas and a Mexican soldier were killed in a shootout on a small island in a reservoir that forms part of the US-Mexican border, dpa reported.
Mexican media reported Tuesday on the shootout, which happened Sunday.
The Mexican Navy said it found a Los Zetas camp while patrolling the area in the north-eastern Mexican state of Tamaulipas.
"The camp worked as a marijuana concentration hub," the Navy said in a statement.
From there, the drugs were believed to be smuggled into the United States in speedboats.
The Navy seized various weapons, ammunition, uniforms and bulletproof vests.
Falcon Dam, on the Rio Grande separating the United States and Mexico, flows between Tamaulipas and the US state of Texas.
On September 30, Los Zetas allegedly killed a US citizen who was riding a watercraft on the lake with his wife. The woman managed to get away, but the man's body was never found.
In a separate incident in drug-crime plagued Mexico, the army found 180 bodies in a total of five mass graves in the Mexican city of Durango, state authorities said Tuesday. The dead were 168 men and 12 women.
No immediate information was provided about the identities of the killers or their motives.
In the town of San Fernando, in the north-eastern Mexican state of Tamaulipas, 183 bodies have been found in 40 mass graves since early April. Many of the dead were believed to have been Mexicans and migrants forced off of busses as they attempted to transit the state. Los Zetas was suspected in most of the killings there, though the Durango killings are not believed to associated with the earlier murders.
"The hypotheses for the investigation, in principle, are very different from what we saw recently in the case of San Fernando," National Security spokesman Alejandro Poire said Monday, when the gruesome Durango mass graves tally stood at 168.
More than 40,000 people have been killed in Mexico in the last four years in incidents linked to organized crime. Most of the victims are believed to have criminal connections, and in many cases they were never reported missing.