13 Killed in Mexican Lake Battle One marine, 12 gunmen die on Falcon Lake By Polly Davis Doig, Newser Staff Posted May 10, 2011 11:06 AM CDT 5 comments Comments In this image released by the Mexican Navy on Monday, May 9, 2011, a group of marines conduct an operation in an island on Falcon Lake in Tamaulipas, Sunday, May 8, 2011. (AP Photo/SEMAR) (Newser) – Mexican marines stumbled upon a drug gang camp on a Texas border lake on Sunday, triggering a firefight that killed one marine and a dozen Zetas drug cartel gunmen in the country's latest bloodbath. The battle occurred on Falcon Lake, where American David Hartley was presumed to be gunned down by gang members last year, notes the AP. Mexican authorities believe the Zetas were smuggling marijuana into Texas by speedboat. The Zetas are wreaking havoc in Tamilaupas state, where last month mass graves yielded 183 bodies—many of which appeared to be civilians pulled off buses in a recruitment effort. Click for more on the ongoing violence.