During a brief storm last month, a trash boom in the Tijuana River managed to stop 20 tons of trash and debris from entering California. Historically, during rain events in the San Diego-Tijuana region, water flows from south of the border into the U.S. carrying tons of plastic, tires and other debris. Last year, as a way to stop the pollution, a 1,200-foot trash boom was strung across the river bed by Alter Terra, a binational environmental group. Sections of the boom float according to the level of the river — its fence-like partitions stop the trash from flowing farther into the Tijuana River Valley and the Pacific Ocean.