The commander of US forces in Asia says Guam is ill-equipped to handle thousands of relocated troops as part of American marine realignment plans with Japan.
Japan is reviewing a 2006 pact under which the United States would shift some 8,000 troops from Japan's crowded Okinawa island to Guam.
Defending the 2006 plan, the head of the US Pacific Command, Admiral Robert Willard, admits there will also be huge pressure on Guam.
Overall it's estimated that Guam, which has a population of fewer than 200-thousand, would take on up to twenty thousand more people as part of the troop build-up.
Admiral Willard told the US House Armed Services Committee that the pressures on Guam water systems, power systems, waste-disposal systems, sewage systems and other infrastructure will be challenging.
He said that Guam's port was "inadequately suited" to handle ships involved in construction.
President Barack Obama's environment adviser is visiting Guam this week to assess the challenges presented by the planned military move.