The Government Accountability Office told a U.S. Senate panel that the Department of Homeland Security's ability to track all small boats with transponders or in other ways might not be effective.
The GAO says the methods could be limited because of the number of such vessels and the difficulty of identifying threatening actions.
Other problems include challenges involved in getting resources to the scene in time to prevent an attack and the limitations of certain equipment, the GAO told the Senate Committee on Commerce, Science and Transportation.
The GAO's comments, a response to follow-up questions lawmakers asked at a committee hearing on maritime security in July, were reported at Homeland Security Today, a preparedness and security news website.
"With the critical task of mitigating the risk posed by small vessels before the Coast Guard and [Customs and Border Protection], we believe a risk-management approach, coupled with strong intelligence-gathering efforts, would lead to the greatest benefit," the GAO also told lawmakers in its follow-up report.
"Intelligence-gathering efforts at the port level, such as America's Waterway Watch (AWW), should help uncover potential threats before they develop into full-fledged attacks. The program's outreach to over 400 local watch group members in and around the Puget Sound region for the Vancouver 2010 Winter Olympics demonstrated its potential as means of increasing vigilance and communication."
"Moreover," the GAO added, "targeted efforts aimed at protecting critical infrastructure and valuable vessels, along with random escorts and patrols, should help provide deterrence against a small-vessel attack inside U.S. port areas. Offshore intelligence efforts aimed at uncovering smuggling operations should also help to target patrols and interceptions."